This part of the website was conceived as a way of tracing the history of the engine indicator; identifying participating manufacturers and their products; deducing (if possible) how many autographic indicators have been made since Watt's first attempt; and providing a way of dating individual items satisfactorily. The work has now been underway for some years, but is still far from complete; the site has generated extensive correspondence, but this often asks more questions than provides answers.

Please note that some search engines regularly retrieve older versions of this material, generally organised in individual chapters and often three years old. Only the files available here are up-to-date; details of the latest amendments will be found on the imprint page (page 4) of each pdf.

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The engine indicator is a fascinating instrument that records how the pressures in the cylinders of steam and internal-combustion engines change during the operating cycle. Used properly, they can identify problems ranging from bad valve settings to constricted steam pipes. One of the major catalysts in development was the increasing realisation that the steam engine, useful tool though it had proved to be, was inefficient. Many reasons have been advanced to account for this process, but it is probable that — once the Watt-type engine began to replace the old Newcomen 'atmospheric' designs — it could be seen that too much coal was being consumed in relation to output. The first attempts to register pressure generated in the cylinders of steam engines were undertaken with columns of mercury, the levels being judged by the displacement of the metal in small-bore tubes.

watt engine

The advent of the Watt-type steam engine inspired the pursuit of efficiency. The first indicators required careful watching, as the readings could only be taken manually, but it was not long before the automated moving-tablet instrument had appeared.

This method was unsatisfactory, as the mercury often oscillated too greatly for satisfactory recordings to be taken and the glass tubes were prone to break. A better solution was proposed by James Watt (1736–1819), who is customarily accorded credit for defining the 'horse power' and was also the first (as far as we know) to produce a 'stand alone' method of indicating steam pressure within a cylinder. About 1790, Watt produced an indicator in which a small piston, travelling within a brass cylinder, moved a pointer; the greater the pressure, the greater the deflection, which, as the engines of the day were slow running, could be seen by an observer. A skilled man could note the progress of the pressure during the steam phase and also the vacuum produced by the condenser.

The first major improvement in the design of the Watt Indicator was made by an employee of Boulton & Watt, John Southern (1758–1815), who designed the first method of recording the operating cycle of the steam engine automatically. In the summer of 1796, Southern suggested adapting the 'recording indicator' by adding a recording-board or tablet that slid within a supporting frame. A cord attached to the beam pulled the tablet sideways as, simultaneously, the pencil-pointer recorded the rise of pressure in the cylinder on a sheet of paper. As the beam returned, a weight attached to the free end of the operating cord reversed the movement of the tablet. The pencil recorded the cylinder pressure as it dropped to nothing, and in so doing closed the diagram of pressure against time.

The shape of this diagram remained characteristic of indicators made into the present century, the earliest datable survivor being made in January 1803. However, indicators were in perpetually short supply until the 1820s. This was partly because James Watt was a secretive man, obsessed with keeping his ideas from others, and the development of a recording indicator was kept from prying eyes. However, details of one such instrument were published in an 'Account of a Steam Engine Indicator', a letter submitted by 'H.H. junr.' to The Quarterly Journal of Science in 1822. This credits knowledge of the indicator to Joshua Field of Maudslay, Son & Field, and manufacture to a foundry owned by 'Mr Hutton of Anderston', Glasgow. Indicators of this type were made into the 1840s, and the idea of a moving tablet reappeared several times in the late nineteenth century. The culmination was a Wayne design, patented in Britain in 1894.

mcnaught indicator drawings

Drawings of the original McNaught indicator, published in a French textbook in 1844, the year of John McNaught's death. Note that the recording drum is co-axial with the piston. Museum of Making collection.

The first major advance to be made after the reciprocating tablet was the oscillating drum. The credit for this is customarily given to the Scotsman John McNaught—largely on his own testimony!—but circumstantial evidence suggests that the idea may have occurred first to Henry Maudslay.

The original McNaught indicator had the recording drum concentric with the piston cylinder, but the perfected version had the drum on a platform that protruded from the cylinder laterally. A swivelling pulley, known as the fairlead, allowed the cord attached to a suitable part of the engine to approach the indicator at an angle. The McNaught indicator relied on a comparatively steam-tight piston sliding in a tube beneath a large coil spring. When the outward stroke of the engine piston began, the pull on the cord turned the drum through a half-revolution. The admission of steam to the cylinder raised the pencil to make its trace. When the inward stroke of the piston began, a helical spring in the recording drum rotated it back through the half-circle to its starting position. This allowed the pencil to complete its loop.

mcnaught indicator

A McNaught indicator with the recording drum offset from the centre line of the piston, probably made in Glasgow in the 1860s by McNaught's successors. Museum of Making collection.

The McNaught indicator was popular, as it was comparatively simple, easily copied, and acceptable efficient. Many attempts were made to improve it, notably by Duvergier in France and Joseph Hopkinson in England, but many of these experiments sought methods of obtaining continuous diagrams instead of improvements to the basic instrument. From this period, too, came the first attempts to develop the so-called 'lining indicator', which constructed an average diagram from a large number of strips taken from successive engine cycles, and the first integrating 'totalisers', which deduced the cumulative or average values numerically. Once the value of the perfected McNaught rotating-drum pattern had been universally admitted, steam-engine indicators were made in great quantity by many manufacturers. But they were expensive. Regarded as precision tools, they still cost more than four times the average English weekly wage in 1914.

The next great advance was made in the U.S.A., where the first high-speed steam engines had been developed in the 1850s. The advent of the Allen engine, promoted enthusiastically by Charles Talbot Porter (1824–1910), was the catalyst. Porter realised that the McNaught-type indicators being made by the Novelty Iron Works were too prone to vibrate when used at high speed, giving tremulous diagrams that were impossible to interpret, and sought something better. The project was given to consulting engineer Charles B. Richards (1833–1919), who within a very short time had produced a workable design by combining the offset recording drum and the internal coil spring of the McNaught with a system of levers, inspired by Watt parallel motion, that amplified the movement of the piston four-fold. This kept the movement of the piston to a minimum, allowed a short stiff spring to be used to damp vibrations, and kept the instrument as compact as possible.

Elliott-Richards indicator, 1880s

The Richards indicator was the first of the 'amplifying designs', capable of multiplying the comparatively small movement of the piston to give a trace at least four times the size. This particular instrument was probably made by Hannan & Buchanan of Glasgow, in the 1890s. Museum of Making collection.

The Porter-Allen engine and the prototype Richards indicator (made by the Novelty Iron Works) were exhibited at the International Exhibition in London in 1862. There the engine attracted much adverse comment, but proved to work smoothly and in perfect safety-confounding the doom-laden predictions of its many detractors. The indicator was used successfully to test a variety of engines on display, though one or two well-known British engineers refused to have anything to do with it. A trial of a railway locomotive was arranged, and the existence of the indicator came to the attention of Elliott Brothers, renowned as makers of optical equipment. A licence was negotiated, and the first Elliott-Richards indicators appeared in 1863. More than ten thousand of them had been made by 1876, and work continued until the end of the nineteenth century.

The Richards indicator proved to be sturdy and reliable, and was still being used in quantity when Europe went to war in 1914. However, the success of the Porter-Allen engine had begun a quest for ever-greater pressures and ever-increasing speed. Above 250 rpm, even the Richards indicator struggled to provide reliable diagrams. This was largely due to the inertia of the parts in the amplifying mechanism, which were long and comparatively heavy.

The first real successor was the work of the American engineer, Joseph W. Thompson, whose indicator was patented with the backing of the Buckeye Engine Company in 1875. The Thompson amplifier (which embodied a more mathematically correct straight-line approximator than its predecessor) was much lighter than the Richards equivalent, taking the form of the letter 'M', and soon proved to give good diagrams at 350 rpm or more. Consequently, Thompson-type indicators were made by many companies after Buckeye withdrew. The best known are the American Steam Gauge Company, Schaeffer & Budenberg, James Robertson & Sons and Dobbie McInnes. Dobbie-patent instruments were still being made in the 1960s substantially in their original 1898-type external-spring form.

Thompson indicator, 1870s

The Thompson was the first U.S.-made indicator to successfully challenge the Richards pattern. This example was the work of the American Steam Gauge Company. Courtesy of Bruce Babcock, Amanda, Ohio.

The indicator designed by Harris Tabor, patented in the U.S.A. in 1878, offered an alternative to the Richards and Thompson patterns. Made by the Ashcroft Manufacturing Company from the early 1880s, the Tabor relied on a slotted vertical standard to direct the pointer in a straight line. The earliest Tabor was too weak to succeed, but the modified design of 1886 proved to be amply strong enough to compete on level terms with the Thompsons.

Tabor indicator, 1880s

The perfected Ashcroft-made Tabor indicator of the 1880s, made by the Ashcroft Mfg Co. in Bridgeport, Connecticut. Museum of Making collection.

When the Thompson patent lapsed, many other designers tried their hand. This is particularly evident in the U.S.A., where instruments such as the Straight Line (1890), the Calkins (1890) and the Lippincott (1900) all briefly prospered. There was even a place for aberrant designs such as the British Kenyon of 1878 and its U.S. equivalent, the Rae, which used Bourdon-type pressure tubes instead of piston springs; the 1887-patent Bachelder, with its adjustable leaf spring placed horizontally; and the British Simplex of 1894, briefly promoted by Elliott Brothers, which had a tong-like spring.

Crosby perfected pattern

A typical 1895-type Crosby internal-spring indicator, renowned for the light weight of the amplifying mechanism. Indicators of this type were often used with high-speed engines prior to 1914. Museum of Making collection.

If the Thompson system was the most popular prior to 1910, then it was eclipsed by the perfected Crosby indicator thereafter. Made in Boston, Massachusetts, the 1882 Crosby and its strengthened 1895-patent successor were made in large quantities. They had the merit of exceptionally light amplifying gear, much lighter than even the Tabor, and a comparative absence of inertia effects.

By 1900, the first of the external-spring indicators were being seen. The earliest is usually acknowledged as the British McKinnell & Buchanan, patented in 1893 on the basis of the Richards mechanism, but the original Maudslay & Field indicator—sometimes said to date as early as the 1820s—may have taken a broadly comparable form.

Many of the earliest designs were poor compromises, including the external-spring Tabor, the first Maihak and the 1902-type Dreyer, Rosenkranz & Droop pattern. The problem was simply that spring-support standards or rods had to be accommodated on the cylinder cap or platform of an otherwise conventional enclosed-spring design. The ideas made sense financially, but were less acceptable where efficiency was concerned. The external-spring Tabor, patented in 1900 by William Houghtaling, even had the amplifying rod spindle in a separate chamber.

The 'second generation' of external-spring designs had the springs beneath the platform, above an abbreviated piston cylinder, and were also often fitted with vulcanite or similar sheathing to allow springs to be changed when the metalwork was hot. The most successful of these indicators were patented by John Dobbie in Britain and by William Trill in the U.S.A.

Lehmann & Michels external-spring indicator

A post-1918 German Lehmann & Michels Typical external-spring indicator, with the spring above a Crosby-like amplifying mechanism hidden within a protective casing. Museum of Making collections.

'Third generation' external spring indicators returned to springs that were mounted on top of the platform, but often relied on extended piston rods or bifurcated or duplicated amplifying links of Thompson or Crosby type to allow the spring to be concentric with the piston rod. Indicators of this type were made in the U.S.A. in Boston, Massachusetts, by the Star Brass Manufacturing Company (Webster patent), the American Steam Gauge Company (Jerrauld patent), and the Crosby Steam Gauge & Valve Company (Davidson patent); and in Pittsburgh, Pennsylvania, by the Bacharach Industrial Instrument Company (Maihak copies). Both Maihak and Lehmann & Michels made Crosby-type indicators in Hamburg, Germany, in accordance with Wilhelm Lehmann's patent of 1909.

Another idea to see success in the 1920s was the cantilever-spring indicator, a descendant of the Bachelder of 1887 patented in Germany in 1924 by Alfred Adolf von Gehlen of Hamburg and made by Maihak AG. This substituted a robust spring-steel bar for the spring, the comparatively minimal deflection under load suiting the instrument to high speed/high pressure recording. The amplifying mechanism and the pointer were essentially the same as the standard Maihaks, however.

Mechanical indicators such as the Maihak Typ 30 and Typ 50 and the Dobbie McInnes Design No. 4 were still popular in the 1960s. Though their distribution declined as first electric and then electronic analysers became available, they were regularly used to indicate marine diesel engines. Indeed, the two German manufactures, Lehmag (formerly Lehmann & Michels) and Leutert (successors to Maihak) still offer external-spring and bar-spring instruments for this particular purpose.

Internal combustion

The gas engine patented in France in January 1860 by Jean-Joseph-Étienne Lenoir, the first of its type to be exploited commercially (though the underlying ideas had originated in the eighteenth century), finally provided the steam engine with an effectual rival. Lenoir's engine looked like a small horizontal steam engine, but a mixture of gas and air was drawn into the cylinder to be ignited at the half-way point. The near-instantaneous combustion of the charge then thrust the piston to the limit of its travel. Aided by the energy stored in a large flywheel, the motion was then reversed. As the piston returned, a charge was drawn in behind it and fired again. The process was continuous, with two power strokes for each revolution of the crank.

Several hundred Lenoir engines had been made by 1865, though experience had shown them to be prone to overheat and run erratically if the cylinder-wall temperature rose to a point where the charge was ignited prematurely. The overall efficiency was merely four per cent: twice as good as the best steam engine of the day, but still a notably poor return. The Lenoir was doomed to be the plaything of the rich and the few businessmen who saw promise in its technology, yet it was also the catalyst for the development of better designs. These included the odd-looking Otto & Langen gas engine of 1867, with a vertical cylinder and a rack-and-pinion to convert the reciprocation of the piston-fired upward, returned by gravity-into rotary motion. Overall efficiency of fourteen per cent was more that four times that of the Lenoir, and more than 4500 Otto & Langen engines were made in the 1870s and 1880s. Gas-Motoren-Fabrik Deutz had made more than forty thousand of the 1876-type horizontal-cylinder successor by 1895.

By the publication in 1897 of Frederick Grover's book A Practical Treatise on Modern Gas and Oil Engines, internal combustion was so well established that 'Acme', 'Premier' and 'Simplex'—among many others—had become household names. The general design had settled on the classical layout of the horizontal steam engine, with a sturdy bed-frame and a large flywheel, though cylinders could be set side-by-side, in tandem, or at opposite ends of the bed.

Excepting the vehicle and aero engines, which were almost always petrol, gas engines were favoured (at least in Britain) for domestic and light industrial applications. Initial reliance on supplies of 'town gas', drawn from mains piping, was gradually eroded by self-contained 'producer gas' units after 1900. The smallest producer-gas units offered commensurately limited power, but were cheaper and easier to run than steam plant. Most relied on a mix of air and steam passed through anthracite to produce combustible gas that could be fed into the engine cylinder.

Crosby gas engine

An engraving of a 16hp twin-cylinder Crossley gas engine, taken from the British periodical 'Engineering' of 22nd February 1889.

The size of internal-combustion engines grew rapidly. Maschinenfabrik Augsburg-Nürnberg had made 215 'large' engines by 1908, averaging nearly 1200hp; and the largest engine available in Britain in 1909 was a 2500hp horizontal double-tandem offered by the Premier Gas Engine Co. Ltd. By this time, the methods of operation had resolved into two basic single-acting systems: the Beau de Rochas or Otto cycle, which required two revolutions of the crankshaft for each power stroke, and the Clerk cycle that required only one. These are now known generically as the 'four stroke' and 'two stroke' cycles respectively.

Among the first to provide an indicator with anything other than a small-diameter piston and strengthened amplifying gear was Rodolphe Mathot of Brussels, author of the influential Gas-Engines and Producer-Gas Plants (originally published in French in 1903). Mathot was granted British Patent 14896/00 of 1900 to protect an auxiliary clockwork drum that could record the pressures obtained from successive piston strokes. This enabled the researcher to tell not whether each individual stroke was flawless, but if the engine was running consistently.

The patent drawings show the drum mounted on a Schaeffer & Budenberg indicator, but the best-known use of the Mathot patent was made by Dobbie McInnes Ltd of Glasgow. Indicators of this type were still being offered in 1939, though demand had never been large: production is unlikely to have exceeded a few hundred. The Mathot recorder, which contained a roll of paper about twelve inches (30cm) long, gave a trace consisting of a large number of peaks representing the pressures generated during each power stroke.

Among the many people who claimed to have pre-empted Mathot was the Briton Magnus Volk (1851–1937), best known as the instigator of the oldest electrically-powered railway still in use, to whom British Patent 6541/1892 was granted to protect an 'Indicator for Gas and Petroleum Engines'. Other contemporaries included the Frenchmen Albert de Dion and Georges Bouton—renowned for their pioneering work on motor vehicles—who obtained British Patent 2104/03 of 1903 for a complicated modernisation of a moving-tablet indicator (U.S. 754287 is comparable).

Dobbie McInnes continuous recorder

A Dobbie McInnes-made continuous-explosion recorder. Based on the clockwork-driven Mathot design introduced in 1902, this particular Design No. 1-type instrument, D1B-27949, was made c. 1938.
Museum of Making collection.

Another approach led to the maximum- or peak-pressure indicator, exemplified by the French Peloux design of 1903 and the British Okills patented from 1907 onward. These relied on manual compression of a spring, against an index, until the pressure generated in the cylinder was exactly counterbalanced. The value could then be read from the scale.

A typical 1936-type Okill peak-pressure indicator, NKD2 no. 2027, graduated on the metric system. The pressure could be read from the Veeder-Root counter when the spring-loaded pointer visible on the left side of the body stopped vibrating.

The development of the high compression internal-combustion engine during the First World War, particularly for aerial use, presented new problems. Conventional continuous-recording indicators such as the Mathot or the Cippollina (both made by Dobbie McInnes) and the Lanza (made by Crosby) could not be used satisfactorily in the air, owing to the excessive stresses involved, and the optical indicators typified by the Hopkinson and Birstall designs were equally inappropriate outside a laboratory. The first to be used successfully in the air was the Farnboro indicator, developed by the British Royal Aeronautical Establishment in 1919–20 and eventually licensed, in an improved form, to Dobbie McInnes. Relying on a spark generator to mark the trace on paper stretched over a large horizontal drum, Farnboro instruments were still being touted in the 1960s.

Farnboro spark-trace recorder

An early Farnboro spark-trace indicator, from the Dobbie McInnes & Clyde catalogue of 1925.
John Walter collection.


Engine indicators were customarily supplied in sturdy boxes made of beech, mahogany, oak or walnut, though Bacharach of Pittsburgh preferred galvanised sheet-steel. These boxes were all carefully fitted to accept additional springs, scale rules, steam cocks, screwdrivers, wipers and oil bottles. It is widely believed that empty spring chambers or forlorn posts signify that something is missing, but most of the manufacturers had standard box patterns that would hold at least four springs. However, only a single spring was offered with each indicator: additional springs brought in more money. Purchasers who were interested only in the performance of one single-cylinder engine needed no more than the basic spring, but, at the other end of the scale, consulting engineers and the inspectors employed by insurance companies could require a dozen.

Jointed pantographs simplified interpretation of the diagrams by splitting them into narrow vertical strips, and spare pistons allowed an indicator to be used with low-pressure steam or high-pressure internal combustion engines at will.

Some boxes were fitted for reducing wheels, enabling indicators to be used with engines of widely differing strokes simply by altering the diameter of a particular pulley. It seems likely that the earliest designs emanated from central Europe — a Bohemian inventor, Ladislav Stanek of Prague, filed a patent in Germany as early as 1878.

Robertson-Thompson indicator with reducing gear

Robertson-Thompson indicator no. 7099, dating from c. 1907, is fitted with the Lippincott-designed 'Improved Victor' reducer no. 4465. Note the exchangeable wooden pulleys and metal bushes. Museum of Making collection.

The greatest distribution of reducing wheels was ultimately to be found in the U.S.A., where the Lippincott-patent 'Victor' (1897) promoted by Robertson & Sons and the 'Faultless' by Trill (1903) were just two of many. Ironically, reducing wheels were uncommon in twentieth-century Europe, though German manufacturers offered increasingly sophisticated designs in the 1920s and 1930s before briefly reviving them after the Second World War. In Britain, wheels of this type are exceptionally rare—Dobbie McInnes made a few in accordance with a 1901-vintage British Patent granted to Wade, but most Britons preferred to use levers and bars attached to the reciprocating parts of the engine.

Stanek reducing gear

A typical European-type reducing wheel, based on a Stanek design of the 1880s. This particular example was sold with a Lehmann & Michels indicator of the early 1920s, fitted in the same box. The graded exchangeable bushes allow the reducer to be adapted to a range of cylinder strokes. Museum of Making collection.

Analysing pressure/time diagrams was greatly helped by the use of a polar planimeter, a mathematical instrument patented in Switzerland in 1853 by Jacob Amsler. This allowed any area bounded by a single continuous line to be quickly and accurately computed, and was an ideal, if expensive adjunct to the engine indicator. A few planimeters were even boxed with indicators and reducing gear.

This Coffin Averager, no. 1189, bears the marks of the Ashcroft Manufacturing Company of Bridgeport. It is assumed to date from the 1890s. John Walter collection.

Among the best-known of the pre-1914 designs are the Swiss-made Amsler and Corradi, which can be found with the names of distributors or manufacturers such as Elliott Brothers or the Crosby Steam Gauge & Valve Company. Keuffel & Esser planimeters were popular in the U.S.A., though they were originally made in Germany prior to the First World War; far less common were the distinctive Lippincott, Trill and Willis patterns, and the earlier 'Coffin Averager'.

For more details of the history of the indicator, click on the individual images below.

Please note, however, that owing to the size and complexity of each file, the pdfs will display in monochrome.

How many indicators…?

This section has been added in the hope that, ultimately, it will be possible to make a reasonable prediction of the total quantity of indicators that have been made. The work, which will take time to complete, is based on an analysis of serial numbers. So if you have an indicator which is numbered outside the ranges given below for each manufacturer, I'd really like to know!

36 Chardon Street and Jamaica Plain, Boston, Massachusetts, U.S.A.

Incorporated in 1854 as the 'Steam Gauge Company', this metalworking business was claiming by the 1890s to be the sole manufacturer of the 'American Thompson Improved Indicator'. An advertisement in Cassier's Magazine for August 1894 claimed that over five thousand indicators had been made, and that they had been 'adopted by the United States Navy for use on all the new Cruisers and Gunboats to be built'. The advert notes the company's products—in addition to the indicators—as pressure gauges and vacuum gauges, water gauges, gauge cocks, whistles, revolution counters, marine clocks, pyrometers, hydrometers, salinometers and 'all instruments incidental to the use of steam'.

1. Richards type
Observed number: 440
Possible number range: 1 to 75

2. Internal- and external-spring Thompson types
Observed numbers: 99 to 8886
Possible number range: 1 to 9500
Notes: these indicators are believed to have been contained in one series, observed numbers being from 99 to 8723 (internal spring) and from 5864 to 8986 (external spring). The same range may extend to include the U.S. Schaeffer & Budenberg-type external-spring indicators (q.v.) which replaced the American Steam Gauge Thompson c. 1915
Estimated total production: 9500

111 Liberty Street, New York City (sales office), and Bridgeport, Connecticut, U.S.A.

Founded in 1851 as the Ashcroft Steam Gauge Works, this metalsmithing business was the sole maker of Tabor indicators 'Approved and Adopted by the U.S. Government on all the New Cruisers', according to the August 1894 Cassier's Magazine (but see also 'American Steam Gauge Company'!). Ashcroft also made steam- and vacuum gauges 'with patent seamless drawn tube', steam traps, marine clocks, test gauges, and all instruments 'for measuring steam, air, gas or water'.

1. Tabor indicators, inside-spring type:
Observed numbers: 227 to 6281
Possible number range: 1 to 6625.
Notes: production may have ceased early in favour of the external-spring instrument, though it is more likely that the two co-existed for a few years. However, it is assumed that only a single number series was used.
Estimated total production: 6625.

2. Tabor indicators, external-spring type:
Observed numbers: 6035 to 10025
Possible number range: 6025 to 11000.
Notes: see (1), above. If the designs co-existed, there would have been more inside-spring and fewer external-spring examples.
Estimated total production: 4975.

Pittsburgh, Pennsylvania, U.S.A.

1. Maihak-type spring type:
Observed numbers: 50791 to 56246
Possible number range: 50001 to 60000?
Notes: numbered in a single series, with the possible exception of the bar-spring type (one reportedly numbered 99675 [59675?]). A standard instrument has been reported with a number in the very low 40000s.
Estimated total production: 10,000+

2. Premax peak-pressure indicator:
Observed numbers: 999 to 2650
Estimated total production: 3500+

3. Cookco Ball-Check Indicator:
Made to a Bacharach patented design.
Observed number: A0662C
Estimated total production: 1000+

Buffalo, New York State, U.S.A.

New York City, U.S.A.

1. Bachelder indicator
Observed numbers: 690 to 3090
Possible number range: from '1'?
Notes: two different types of instrument, the original and an improved Thompson-linkage type
Estimated total production: 3500+

(later '& Son', then '& Son Ltd', and then apparently '& Son' again).

Trading in the 1890s from Market Street, Manchester, England, this instrument-making business made a variety of indicators. A directory produced during the First World War records that 'J. Casartelli & Son, of Hayes Yard Works, Garratt Street, Manchester' were 'opticians and instrument makers' specialising in 'Mining dials, engine indicators, &c'. The company employed 28 people in 1917.

1. Mixed internal and semi-external spring types:
Observed numbers: 45 to 3412
Possible number range: 1 to 5000+ (see notes).
Notes: the Casartelli indicators seem to form a continuous series (with the exception of the rare unnumbered ... pattern). Casartelli-Richards instrument no. 5010 has been reported; this is clearly not an Elliott-made piece from the 1870s, but whether it could date as late as 1920 (as predicted by the number) seems questionable. In addition, as with so many of the instrument makers, it is not entirely clear if telescopes and other items were numbered in the same sequence as the indicators. Consequently, the total given here could be considerably overstated.
Estimated total production: 3500.

Corry, Pennsylvania, U.S.A.

Purchaser of the business of William Trill (q.v.) in 1945. It is not known if production of indicators continued (Corry became known for oxygen regulators for the aircraft industry), but it is at least likely that some were assembled from existing parts. Repairs to Trill and other indicators were certainly undertaken for some years. The Corry Manufacturing Company, which is still trading, was an outgrowth of the instrument-making business.

38 Central Street, Boston, Massachusetts, U.S.A.

A manual for the patented reducing wheel, dated December 1918, gives the addresses of the Crosby offices as 44 Dey Street, New York; 180 North Market Street, Chicago; and 147 Queen Victoria Street, London E.C. In addition to indicators, Crosby made a wide range of accessories, including three-way steam cocks, large-diameter and continuous-recording indicator drums, and two types of reducing wheel (the original of c. 1900 and a New Model introduced in 1918).

1. Internal-spring type:
Observed numbers: 158 to 15837
Possible number range: 1 to 16000.
Notes: numbered in a single series.
Estimated total production: 16,000.

2. External-spring type, first pattern:
Observed numbers: 0391 to 01323
Possible number range: 1 to 01500.
Notes: numbered in a separate series. The oldest known are numbered '31-S' and '32-S', but the significance of this is currently unknown as no major differences in design have been reported.
Estimated total production: 1500.

3. External-spring, second pattern:
Observed numbers: 142D to 7249D
Possible number range: 1D to 7500D.
Notes: numbered in a separate series.
Estimated total production: 7500.


Glasgow, Scotland

The company had its origins in the business of Alexander Dobbie (1815-87), a watch- and clockmaker who began trading from 20 Clyde Place, Glasgow, in 1841. By 1851, Dobbie was listing himself as a maker of nautical instruments and a seller of maritime charts in addition to his horological interests. The census of 1851 recorded that Dobbie, described as a 'Master Chronometer Maker', employed six men and two apprentices. A move to 24 Clyde Place occurred in 1857, the adjoining No. 25 being added in 1873. This was apparently a consequence of the disastrous explosion in Tradeston Flour Mills, which had flattened the workshop in the summer of 1872, a number of Dobbie’s workmen being among the injuries. A branch office at 31 Centre Street was also maintained from 1886 onward.

Alexander Dobbie was joined in the 1880s by his youngest son, John Clark Dobbie (c. 1855-1910). In 1886, the company became 'Alexander Dobbie & Son', but the elder Dobbie died on 18th February 1887 and John Clark Dobbie—by then being described as a 'nautical instrument maker'—succeeded to the business by buying out his father's share after an agreement with the executors. A period of enlargement followed, with retail premises being opened in Commerce Street and a new workshop created at 120 Broomielaw. A move to 44 & 45 Clyde Place occurred in 1892, formerly the premises of the moribund M. Walker & Son. The Broomielaw workshop was then closed, but Dobbie continued to prosper.

The most important acquisition, in 1893, was the business and goodwill of Thomas Struthers McInnes (q.v.), following the death of the proprietor in 1892 and the sequestration of his business. Operations were reconstituted as 'T.S. McInnes & Co. Ltd', work continuing in the original workshops independently of Alexander Dobbie & Son. An associated business opened in London in 1894, trading as 'Dobbie, Son & Hutton', and the trading style of the parent company became 'Alexander Dobbie & Son Ltd' in 1896. More subsidiaries followed: shops at 28 Cathcart Street, Greenock and in South Shields were opened in 1897, and 'Dobbie, Hutton & Gebbie' was formed in Cardiff in 1899. Finally, in 1903, an amalgamation of the two separate interests produced Dobbie, McInnes Ltd. A new head office was opened at 45 Bothwell Street (moved to 57 Bothwell Street in 1908), and a branch was opened in Liverpool in 1907.

The Dobbie workshop continued to make watches, clocks and nautical instruments, as well as being 'chemical, mathematical, optical and philosophical instrument makers' (according to Angus McLean, Local Industries of Glasgow and the West of Scotland, 1901); the McInnes portion continued to make steam-engine indicators and associated engineering equipment. John Clark Dobbie received twenty patents in 1887-1910, ranging from improved indicators to a ship's log and mariners' compasses. The indicators were habitually known as 'McInnes Dobbie' until the end of the First World War, and as 'Dobbie McInnes' thereafter.

John Clark Dobbie died in 1910, to be superseded by his son Alexander B. Dobbie, though his eldest brother, Professor Sir James Dobbie (1852-1924), became chairman—apparently only after the end of the First World War. A directory produced during the First World War notes the company's pre 1914 output as "Engine (steam and Diesel, &c.) indicators. Pressure and vacuum gauges, steam and mechanical specialities for engine testing and equipment. Ships' compasses, sounding machines, and nautical instruments generally". The company was employing 164 people in Bothwell Street and a workshop in Broomloan Road, Govan.

Dobbie McInnes & Clyde Ltd succeeded Dobbie McInnes Ltd in 1921. The enclosed-spring Patterns 'A' and 'B' indicators were largely abandoned, though individual sales were still being made as late as 1940. However, production of the exposed-spring McInnes Dobbie No. 1A (1898 patent) indicators continued with few important changes—though work on the No. 2, No. 3 and the improved 1904-patent or 'caged spring' types ceased. The markings on the instruments changed to 'Dobbie McInnes' to reflect the change in company structure. On 1st January 1937, 'Dobbie McInnes & Clyde Ltd' reverted to the original name. Dobbie McInnes continued work after the end of the Second World War, under the guidance a Nobel Prize winner, the chemist Sir Norman Haworth (1889-1950, son-in-law of Sir James Dobbie); eventually, however, Dobbie, McInnes was swallowed in 1984 by the Cunningham Shearer Group and its operations merged with Young & Cunningham.

1. Mixed internal- and external-spring types:
Observed numbers: 735 to 33398, 45027 to 48587
Possible number range: 1 to 50000.
Notes: in a single series, numbered from 1, probably skipping numbers from about 35000 to 45000. With the break for Dobbie McInnes & Clyde between 19121 and 21080; and a reversion to Dobbie McInnes between 25378 and 26668.
Estimated total output: 40,000.

2. Hopkinson flashlight indicator:
Observed numbers: 58 to 183
Possible number range: 1 to 250?
Notes: in a separate series.
Estimated total production: 250.

3. Farnboro spark-trace indicator:
Observed number: GM 764
Possible number range: not known.
Notes: probably numbered in a separate series, but may, perhaps, have run on from the Hopkinsons.
Estimated total production: 750.

4. Sulzer-type peak-pressure instruments:
Observed numbers: 1184 to 4776
Possible number range: from '1' or '1000'?
Notes: 'observed numbers' for ECPC indicators. It is assumed that ECPB instruments lay at the beginning of the series, but evidence is still lacking
Estimated total production: 5500.

('Dreyer, Rosenkranz & Droop AG' from 1922)
Hannover, Germany

The most important of the pre-1900 German indicator makers, eclipsing Schaeffer & Budenberg, largely owing to an 'improved Thompson' tracing mechanism designed in the early 1880s by Philipp Rosenkranz (author of one of the most successful indicating-practise textbooks). However, the earliest external-spring DR&D indicators were clumsy and could not compete effectively with the Lehmann-designed Maihaks of 1908 which were being sold in substantial quantities when the First World War began.

Dreyer, Rosenkranz & Droop introduced simplified external-spring indicators in the early 1920s, with a distinctive conical spring-support standard, but even these lost ground to Maihak and Lehmann & Michels (making what was essentially the same design). In addition, the owners of DR&D had Jewish connexions, and, almost as soon as the Third Reich had been formed, lost their influence. The ultimate fate of the company is unknown, but it is assumed to have been 'transferred' to more poltically acceptable owners.

Observed numbers: 728 to 13589
Possible number range: probably from '1'.
Notes: to add.
Estimated total production: 20,000+.

449 Strand and 101-102 St Martin's Lane, London, England.

This long-established mathematical and optical instrument maker was responsible for a broad range of indicators—including Richards, Darke, Wayne and Simplex patterns. However, the British market seems to have been surrendered to Dobbie McInnes Ltd (q.v.) and few Elliott-made examples can be reliably dated later than 1910.

1. Richards-type indicators:
Observed numbers: 137 to 18113
Possible number range: 1 to 23000
Notes: indicator no. 22007 has been reported, but not yet verified.
Estimated total production: 23,000?

2. High-speed Elliott-Darke indicators (small and large):
Observed numbers: (small) 30 to 2759, (large) 8368 to 11637
Possible number range: 1 to 12500
Notes: it is is suspected, owing to the apparent gap between the highest 'small' number and the lowest 'large' number, that the indicators were nuimbered in two separate sequences.
Estimated total production: 7000

3. Simplex indicators:
Observed numbers: 453('A') to 918('B')
Possible number range: 1 to 1000
Notes: in a separate series. It is assumed that 'A' (large) and 'B' (small) instruments were numbered together, though evidence is lacking.
Estimated total production: 1000

Jamestown, New York, U.S.A.

Manufacturers of the Excelsior and Howard-Thompson indicators. Succeeded by the Engineering & Power Company (below), c. 1902. Observed numbers range from 151 to 336.

Jamestown, New York, U.S.A.

Manufacturers of the Excelsior and Howard-Thompson indicators in succession to the Engineering Appliance Company. Succeeded in turn by the Trill Indicator Company, c. 1910. Observed numbers range from 4503 to 4993, but it is not clear from the meagre available data if the series began at '1'.

New York City, U.S.A.

1. Calkins internal-spring type
Observed numbers: 23 to 152
Possible number range: 1 to 250?
Notes: to add.
Estimated total production: 250.

Paris, France.

A renowned clock- and watchmaker, Garmier and his son (also named Paul) made a variety of indicators. These were often on a one-off basis for trials with the Conservatoire des arts et métiers or the Academie Française. Garnier indicators included copies of the McNaught, including some 'lining' examples; the Martin piston-type indicator, with a Thompson amplifying system; a disc-pattern Martin; and the Deprez lining design. A solitary exposed-spring indicator, essentially similar to the German Stauss and Lehmann/Maihak patterns has also been found. Its age and rarity are difficult to determine satisfactorily.

Helen Street Engine Works, Govan, Glasgow, Scotland.

This marine engineering business began trading in Helen Street in 1893, but failed in 1901 after making distinctive Thompson-type indicators from c. 1895 onward. It was succeeded by A. Rodger & Co., active on the same site until 1912.

1. Thompson-type internal-spring instruments:
Observed numbers: 296 to 1295
Possible number range: 1 to 1500.
Notes: only five of these 'Type A' indicators have been recorded.
Estimated total production: 1500.


Robertson Street, Glasgow, Scotland (in 1905).

This mechanical engineering business was formed in 1861 as 'John Hannan (Engineers)', trading from 31 Robertson Street until becoming 'Hannan & Buchanan' in 1869. The premises moved to 75 Robertson Street at much the same time, where work continued until 1966. These instrument-making businesses made and/or sold standard McNaught-type indicators; modified a few Richards indicators purchased from Elliott Bros. (and, therefore numbered in the Elliott ranges); and then made Richards indicators in large numbers until 1914 or later. A small-scale 'high speed' Richards derivative was also developed.

McKinnell & Buchanan external-spring indicators and Thompson-type instruments were made in the 1895-1906 period, the latter with three-digit numbers ('103', '104'), but it is assumed that production was negligible. No H&B Thompson is known to survive.

Estimated total production: 10,000+, assuming that indicators were numbered in a series of their own, and not with any other instruments marketed by Hannan & Buchanan.

New York City, U.S.A.

1. Arc and Straight-Line indicators
Observed numbers: (Arc) 211 and 229; (Straight Line) 512 to 3106
Possible number range: from '1'?
Estimated total production: uncertain.

2. Thompson type
Observed numbers: 200 to 8038
Possible number range: 1 to 9000.
Notes: numbered in a single series.
Estimated total production: 9000.

Huddersfield, England

Hopkinson made a concentric-axis indicator (no numbered survivors have yet been reported) and then a non-amplifying 'Model 1869' version with an offset drum (five numbered from 211 to 708 with a sixth said to be no. 1029). He was claiming to have sold 1200 indicators by 1875, but confirmation is lacking and it is just possible that other instruments were included in the number series.

Estimated total production: 1250.

Paris (?), France.

Made Thompson-type indicators in 1880-95, including a patented improvement with the piston spring isolated in a separate ventilated chamber.

Hamburg(-Altona), Germany

Lehmann was the designer of the pre-1914 Maihak exposed-spring indicator (the British Patent was granted in his name), which had succeeded the short-lived Staus pattern in series production by 1908. These instruments were made in several sizes, but apparently only after 1919. Most of the earliest, perhaps owing to a desire to promote them in Britain and France do not bear any marks other than a number. Improved versions, including a 'High Speed' derivative, appeared in the 1920s and an improved form of the Typ 50 is available even today!

Observed numbers: 1576 to 5205
Possible number range: from '1'
Notes: the numbering system seems to have changed after the Second World War, possibly starting again (at 50000?). It has been suggested that the first two numbers are a 'date prefix', but too few instrumentshave been examined to decide.
Estimated total production: 50,000?

Successors to Maihak (q.v.) in the 1970s. Production of the Typ 30 and Typ 50 Lehmann-type indicators continued alongside a variety of peak-pressure instruments including a mechanical pattern originating in the 1950s.

Observed number: 50Z1 94389
Possible number range: apparently runs on from the Maihaks.
Notes: to add.
Estimated total production: 50,000?

New York City, U.S.A.

Observed numbers: 1010 to 9056
Possible number range: 1 to 10000.
Notes: all apparently numbered in the same series (external-spring indicators currently confined to the 8045–8075 block).
Estimated total production: 10,000.

Bexley, Kent, England.

Made Little's Patent Integrating Indicator from about 1897 until shortly before the First World War, though output was never large (no more than 50?). Only a single indicator has been traced, but does not seem to display anything that could be considered as a serial number.

or M’Innes
Glasgow, Scotland (1889-1903).

Thomas Struthers McInnes, a maker of nautical instruments, began trading from 56 Waterloo Street, Glasgow, in 1889—perhaps succeeding a short lived partnership of McInnes & Cairns. The trading style became 'T.S. McInnes & Company' in 1890, a move to 86 York Street and 341 Argyle Street occurring in 1892. McInnes died in 1893, when the assets of his business were acquired by John Dobbie. The name then changed again to 'T.S. McInnes & Co. Ltd' in 1894, based at 41 Clyde Place (listed as 41 & 42 Clyde Place from 1896 onward). In 1903, the McInnes company amalgamated with A. Dobbie & Son to form 'Dobbie McInnes' (q.v.).

1. McInnes internal-spring type:
Observed numbers: 337 to 3642
Possible number range: 1 to 3750.
Notes: McInnes' name has also been found on a Richards-type indicator, no. 244, presumably numbered in the same basic sequence. As McInnes was an instrument maker, it is possible that other items were numbered in the same series as the indicators, and thus that the assessed total is actually over-stated. However, a substantial number of McInnes indicators were sold after the business passed to Dobbie in 1893.
Estimated total production: 3500.


Though McNaught is generally recognised as the designer of the indicators that are now widely associated with his name—the original concentric type and the later version with an offset paper drum—the instruments were the work of many mid-nineteenth century instrument makers (Chadburn, for example). Total output is unlikely to have been large, perhaps no more than 500-800, but an almost universal absence of numbers remains a barrier to accurate cataloguing. McNaught's own contribution remains equally unclear.

Estimated total production: a hundred?

('H. Maihak AG' from 1910)
Hamburg, Germany

It seems that Hugo Maihak began trading in the 1880s, as a distributor of engineering accessories. Among these were pressure gauges made by Crosby (q.v.), and substantial numbers of Crosby indicators were also imported for sale in Germany. Eventually, presumably when a fixed-term agreement had lapsed, Maihak made a near-copy of the inside-spring Crosby in Hamburg.

When Crosby introduced the external-spring Davidson design, Maihak, probably fearing that sales would be lost, introduced a comparable indicator designed by Wilhelm Lehmann.

Lehmann was apparently the manager of the Maihak manufactory; the indicator was patented in his own name in Britain, but the German and some other patents name only Maihak (to whom the British Patent was assigned).

The inside-spring Maihak indicators were made in conventional or high-speed form, the latter with a short over-centre trace-arm curved somewhat like the Dobbie McInnes design. Production was comparatively small, as Maihak moved first to the Stauss indicator and then to the Lehmann, which was being made in four sizes when the First World War began.

Improvements were made in the early 1920s, when the four original patterns gave way to Typ 50 and Typ 30 (the numbers refer to the diameter of the paper drum), supplemented by a high-speed diminutive of the Lehmann indicator and the unique bar- or rod-spring Gehlen design sold as the 'Typ S'. Production continued throughout the Second World War, though the quality of finish, in particular, declined. It seems probably that very few indicators were made after 1943, and that most of those that were sold in the immediate post-war years came from pre-1945 stock.

However, production began again (perhaps in 1950) and a healthy trade was re-established. The Typ 30, Typ 50 and Typ S continued to be offered, alongside peak-pressure indicators (mechanical and then electronic), until this particular part of the Maihak business was sold in 1981 to Leutert (q.v.).

1. Internal-spring Crosby type.
Observed numbers: 2027. Possible number range: from '1' or '1000'?

2. External-spring Stauss type.
Observed numbers: none. Possible number range: unknown, but probably in the Crosby sequence.

3. External-spring, Lehmann type
Observed numbers: (pre-1945) to 42760; (post-1950); typically 30-54323and 50Z-53399.
Possible number range: the pre-1945 guns probably ran on from the Crosby copies. 'New' or post-1950 production may have been numbered from 50001.

4. Gehlen bar-spring type
Observed numbers:
Possible number range: likely to have been within the resgular sequence, but with an 'S'-prefix.

Notes: it is assumed that all the Maihak indicators made prior to 1939 were numbered in a single series. It has been suggested that post-1945 instruments were numbered with what is either a two-digit 'year' prefix or a new cumulative sequence. However, it seems clear, from a few correlations with order numbers and dates on some springs, that the 'single sequence' system is more likely to have been used.
Estimated total production: 50,000+

Meerane in Sachsen, German Democratic Republic

Formed soon after the end of the Second World War, this state-owned engineering business made a variety of external-spring indicators. Catalogues normally acknowledge a debt to Crosby, as Metallwerker used an essentially similar Lehmann-type recording mechanism found on the Maihak and Lehmann & Michels instruments. A feature of this particular range was the spectacular variety of piston options; a similarly wide variety of springs; and accessories such as remote-release devices and continuous-roll drums.

A 1963-vintage catalogue produced on behalf of the principal distributor, Deutsche Export- u. Importgesellschaft Feinmechanik Optik GmbH (of 'Berlin C2, Schicklerstrasse 7'), noted that Metallwerker made ''Torsograph, Vibrograph, Tachograph, Extensograph, Registrierappärate, Tastograph, Spezialappärate'. The indicators were minor modifications of the Lehmann design.

Observed numbers: none.
Possible number range: not known.
Notes: no indicators of this type have yet been reported in detail. It is possible that up to five digits were used, but confirmation is lacking.
Estimated total production: 25,000?


Observed numbers: 89522, 90100
Possible number range: not known
Notes: to add.
Estimated total production: 20,000+

New York City.

The first manufacturer of indicators active in the U.S.A., Novelty made McNaught-type designs. One of these survives in the Smithsonian Museum collection.

204 Fulton Street, New York City, with 'Branch Offices in Boston, Philadelphia, St. Louis'.

This well-established metalworking business made a variety of indicators, patenting attachments such as the 'Pneumatic device', allowing two indicators to be operated simultaneously, and the 'Take-Up Device for use in connection with Detent on Indicator' in May 1895 and June 1901 respectively.

1. Robertson-Thompson internal-spring indicators
Observed numbers: 261 to 8308
Possible number range: from '1'.
Estimated total production: 9000?

Magdeburg, Germany, and elsewhere

This well-known engineering company, with branches in Britain and the U.S.A. in addition to Germany, was originally formed to exploit a riband-spring pressure gauge patented in 1849 by Bernhard Schaeffer. The original partners were Schaeffer himself, Christian Friedrich Budenberg (1815-83), and Franz Primaveri, a master mechanic. Trading in Magbeburg as 'Schaeffer & Co., Mechanische Werkstatt' continued until Primaveri left the business in 1852 and the style 'Schaeffer & Budenberg' was adopted. A move to Buckau, then a village several kilometres from the centre of Magdeburg, occurred in 1859.

The company initially concentrated on Schaeffer-type pressure gauges, changing to the Bourdon pressure-tube design as soon as patents protecting the French design lapsed in the mid 1860s. The success of these products (particularly in Britain from 1853 onward) allowed Schaeffer & Budenberg to grow rapidly. An agency was established in Manchester in 1857 by Arnold Budenberg, brother of Christian Friedrich, initially to meet the demands of the Lancashire cotton industry but later to supply the needs of not only the British Empire but also the U.S.A.

The success of the Bourdon-type pressure gauges then persuaded the Schaeffer & Budenberg management to begin assembly not only in Manchester but also in New York from c. 1873 onward. Most of the components were supplied from Buckau. However, a factory was opened in Whitworth Street in Manchester in 1896 and there is no doubt that many components were made there; the same seems to be true of the New York establishment, which was enlarged at this time.

By 1914, the company was operating factories in Buckau (which had become an administrative district of Magdeburg in 1887), Manchester, New York, Paris, Lille and Milan. There were depots and sales offices in Vienna, Liege, Prague, St Petersburg, Stockholm, Hamburg, Zurich, Glasgow and London. By 1916, four thousand people (Beschäftigte) were being employed in sixteen different locations (Standorten).

When the First World War began, shortly after Schaeffer & Budenberg had moved from Whitworth Street in Manchester to a purpose-built factory in Broadheath (near Altrincham, Cheshire), the British operations were sequestered by the British Crown. Work continued under the directorship of British-born Frederick Budenberg—who had succeeded his father Arnold in 1888—to ensure that supplies of the gauges and machinery that were vital to the war effort were still being distributed throughout the British Empire.

In March 1918, Frederick Budenberg, who was by then a British citizen, was allowed to buy the British branch of Schaeffer & Budenberg back from the British Crown and re-registered it as the 'Budenberg Gauge Co. Ltd'. Almost as soon as the war ended, however, boiler fittings, valves, hooters and whistles, indicators, measuring instruments and pumps were once again imported from Magdeburg-Buckau to be sold alongside pressure gauges made in Britain.

Frederick Budenberg died in 1941, to be succeeded by his son Christian Frederick. The business was once again placed under government control, making a variety of pressure gauges and hydraulic operating systems until 1945. The German shareholding was then finally liquidated. Pressure gauges, dial thermometers and valves were made so successfully that a new factory was opened in Amlwch (Wales) in 1963 and a manufacturing subsidiary was formed in Australia, but the Budenberg family sold the business to Burnfields Ltd in 1991. Finally, in 2002, the Budenberg Gauge Co. Ltd moved from Altrincham to Irlam, on the outskirts of Manchester.

After the end of the Second World War, Schaeffer & Budenberg GmbH ceased to trade. However, operations recommenced in what was to become the German Democratic Republic—initially as Magdeburger Armaturenwerke ('MAW') and then as VEB MAW 'Karl Marx'.

Observed numbers: 221 to 21275
Possible number range: from '1'
Notes: very few details of post-1920 production (nor details of the serial numbers of indicators) have yet been found.
Estimated total production: at least 25,000

66 John Street, New York City, and 22 West Lake Street, Chicago, Illinois (salesrooms); Brooklyn, New York (factory).

The North American arm of the well-known German manufactory, this made the 'Improved Thompson Indicator', 'adapted for all speeds, unsurpassed for Simplicity, Reliability, and Excellence of Workmanship. Sold at moderate prices'. S&B also made tachometers, pressure gauges 'for all purposes', engine counters and registers, marine clocks and thermometers, the Peerless and Manhattan injectors, together with reducing and regulating vales (according to Cassier's Magazine of August 1894). A later Schaeffer & Budenberg 'American' catalogue, which includes the external-spring design, also noted the 'American Ideal Reducing Wheel' among the company's products.

31 Lancaster Street, Boston, Massachusetts, U.S.A. (saleroom and factory); 28 New Bridge Street, London EC, England (saleroom, listed in 1905).

Listed in the August 1894 edition of Cassier's Magazine as a maker of steam-, water- and vacuum gauges, 'with non-corrosive movements', Star also made revolution counters, marine- and locomotive clocks, sight-feed lubricators and oil cups, 'pop' safety valves, and 'boiler appliances in general'. The name has also been linked with indicators, a relevant patent being granted in Britain in the 1890s.

1. Internal-spring indicators:
Observed numbers: 113 to 212
Possible number range: 1 to 300
Notes: to add
Estimated total production: 300?

2. External-spring indicators:
Observed numbers: 654 to 735
Possible number range: 300-1000?
Notes: to add.
Estimated total production: 700?

Empress Foundry, Cornbrook, Manchester.

This foundry and engineering business made at least two hundred of Kenyon's Patent Pistonless Indicator (c. 1880-5). By 1917 the business, losing its independence, had become part of United Brass Founders & Engineers.

All Saints Works, Bolton, Lancashire, England

Makers of the various Okill peak-pressure indicators from before the First World War into the 1960s.

Observed numbers, perfected design: imperial, 6035 to 9822; metric, 2027
Possible number range: from '1'?
Notes: the Okills seem to have been numbered in at least three groups—the original 'P' series (P515); the New Model (91); and the perfected types, which are probably in separate imperial and metric series (judged by the style of the counters).
Estimated total production: 13,500+

New York, U.S.A.

Trading in August 1894 from 110 Liberty Street, New York City, after a then-recent move, this partnership made the Bachelder Adjustable Spring Indicator, 'for any speed or pressure', and the Ideal reducing wheel. The advertisement lists other products as "Grimm's Patent Injector Blower, and Thompson's Patent Soot Sucker for cleaning Boiler Tubes. Shaking, Interlocking and Sectional Grate Bars, Steam Specialities and Supplies…"

1. Bachelder indicator
Observed numbers: 353 to 636
Possible number range: from '1'.
Notes: to add.
Estimated total production: not known.

Corry, Pennsylvania, U.S.A.

Founded by William L. Trill in 1901, this metalworking business made a selection of internal- and external-spring indicators. Trade is said to have declined after Trill's death in 1943, though employees continued to work until the end of the Second World War. The moribund Trill business was then purchased by the Corry Instrument Company (q.v.). Production is difficult to assess, as Trill never numbered its internal- and external-spring indicators individually. Allowing for an increase in output for the 1942-5 era, total production may have been in the region of 16,000.

Glasgow, Scotland.

Renowned as a maker of nautical instruments, this business traced its history back to a move from Greenock to Glasgow by nautical-instrument maker David Heron (1827) and the formation in 1836 of 'David Heron & Company'. After a chequered trading history, including two bankruptcies, Heron relinquished in 1864 control of what was originally a 'Ship Chandlery and Nautical Ware House' (but had become a compass adjuster and nautical-instrument maker) to his son-in-law, James Whyte. Whyte seems to have taken James Thomson as an apprentice, and Whyte & Company, formed in the 1870s, became 'Whyte, Thomson & Company' in 1889.

Premises were maintained at 144 Broomielaw, with a workshop (Neptune Works) in Harmony Row, Govan. Subsequent moves of the offices included 96 Hope Street (1912), 159 Queen Street (1923), 47 Cadogan Street (1927) and 57 Bothwell Street in 1934. The workshop remained in Harmony Row until 1915, when it was relocated in North Woodside Street until moving to 191-3 Broomloan Road in 1948.

The founding owners of Whyte, Thomson & Co. were James Thomson and James Whyte, Junior. A branch was maintained in South Shields from 1902 until 1916, and trading continued until 1934. James Thomson and James Wilson then helped to create Christie & Wilson, and William D. Whyte re-formed the original operations as 'Whyte, Thomson & Co. Ltd', which continued to trade until 1953.

Whyte, Thomson & Co. gained a silver medal at the 1886 Edinburgh exhibition, showing, according to the Official Catalogue, a variety of "Nautical instruments…for ships' use. Binnacle Stands and Compasses for yachts etc. Lifeboat Binnacles and Spirit Compasses…, Clinometer, Salinometer, Sextants, Chronometer Clocks, Telescopes, Thermometers, etc." A claim that 'pressure gauges, vacuum gauges, engine counters and indicators, lamps and cabin fittings' were being made, on the basis of an entry in Glasgow and Its Environs (1891), suggests that indicators were made in comparatively small numbers prior to the First World War.

Whyte, Thomson & Company employed more than seventy people in 1891. Manufacturing facilities were undoubtedly maintained even though evidence suggests that instruments were regularly acquired from other Glasgow makers to fulfil urgent orders. Two of the addresses given on Whyte, Thomson ephemera—57 Bothwell Street, 191-3 Broomloan Road—are those of Dobbie McInnes, and it is clear that Whyte, Thomson & Company had an agreement with their landlords until trading finished shortly after William Whyte died in 1953.

Observed number: 351
Possible number range: not known.
Notes: only a single Whyte, Thomson indicator has been found. It is suspected (but not confirmed) that other instruments were included in the numbering series.
Estimated total production: not more than 100.