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Kew Watch Trials

The observatory at Kew in Richmond, Surrey, was commissioned in 1769 by King George III for the purposes of conducting astronomical observations. However, the facility was soon used for testing watches, or at least one watch. Between May and July in 1772, John Harrison's H5, a replica of the watch called H4 that was taken by Harrison's son on the famous voyage to Jamaica, was tested at the King's Observatory where it too produced a phenomenal performance.

Less exalted watch trials were begun in 1884 at the Kew observatory under the direction of the Kew Committee of the Royal Society to rate watches and box chronometers on a similar basis to the observatories at Geneva and Yale. The Kew trials were extended to include complicated watches such as chronographs, initially at the request of the Cyclists Union and later for the Metropolitan Police for motor car speed checks.

The Kew trials were not connected with the trials of box chronometers and deck watches that had been performed at Greenwich since 1820 for the purpose of selecting timekeepers for the Royal Navy and land survey use.

Stauffer Advertisement October 1891.
Stauffer Advertisement October 1891.: Click image to enlarge

The original intention of the Kew watch trials was to promote English watches and drive technical improvements, probably with the idea of demonstrating the high quality of English watches to cock a snook at pesky foreigners. However, Swiss watch manufacturers were not slow to spot an opportunity to gain credibility in one of the their most important export markets. They soon started to enter watches for the trials and quickly came to dominate the results.

Watches could be entered for trial in one of three categories, A, B or C. Marks were awarded for performance and watches that passed the trial were awarded a certificate showing which category trial had been passed, hence Kew A, B or C certificates.

The fees for the three classes were one guineau (21 shillings or £1.05 in decimalised currency), 10s 6d, and 5s 6d respectively. If a watch failed to obtain a certificate in the class for which it was entered, half the fee was charged. At the time, good watch with a silver case retailed at around £5, which meant that the trial, especially Class A, was expensive for watch manufacturers.

The Class A trial was the most demanding and most competitive, with the results being closely studied and used in advertising. The Class B and C trials were less demanding, but were still taxing for watches of the time, so a Kew certificate of any class is well regarded.

For the first years the results to the end of October were reported in the following January, but from 1892 results to 31 December the previous year were usually reported in March. The 1893 report was delayed to May by the untimely death of Mr Whipple.

Kew Class A Records
YearMakerEscapementMarks
1885 E. F. Ashley Fixed86.1
1886 E. F. Ashley Fixed86.7
1887 Jos. White Fixed88.1
1888 W. Holland Fixed89.0
1889 E. F. Ashley Fixed89.1
1891 Stauffer & Co Tourbillon91.6
1892 Baume & Co Tourbillon91.9
1902 H. Golay Tourbillon92.7
1903 P. Ditisheim Tourbillon94.9
1912 P. Ditisheim Fixed96.1
1917/18P. Ditisheim Fixed96.2
1919/20P. Ditisheim Fixed96.9
1923/24P. Ditisheim Fixed97.0

For the years 1885 to 1890, English companies held the record for the highest number of marks in Class A, but in 1891 a Swiss watch entered by Stauffer & Co took the record with 91.6 marks, a feat that Stauffer was quick to advertise as shown in the image here.

In 1892, a Swiss watch entered by Baume & Co achieved 91.9 marks, taking the record away from Stauffer. This was initially assumed by some to be a Longines watch, but Baume stated that it was one of their own manufacture.

After 1891 Swiss made watches held the Kew record except for 1902, when a watch entered by Hector Golay, a Swiss born watchmaker working in London, briefly held the record.

The table of Kew Class A records shows each new record high mark. In the years omitted from the table, the highest mark achieved did not exceed the existing record.

It is notable that the record of 91.9 marks set in 1892 by Baume & Co with a going barrel and Tourbillon-mounted chronometer (detent) escapement with a single overcoil balance spring was not exceeded until ten years later in 1902 by Golay, also with watch fitted with a Tourbillon.

Golay's triumph was short lived. In 1903, Paul Ditisheim seized the record with a huge leap of 2.2 marks to 94.9. The watch had a Tourbillon and a Guillaume balance, the first appearance at Kew of this compensation balance that reduced middle temperature error. This was the beginning of Ditisheim's domination of the Kew trial records.

Transfer to National Physical Laboratory

In November 1912, watch testing was transferred to the National Physical Laboratory at Teddington, although the certificates awarded to successful watches continued to be called “Kew certificates”.

In the last set of trials conducted at Kew in 1912, a new record was set by a watch sent by Paul Ditisheim. The report of the year's trials said:

The first place was taken by the keyless, double-roller, going-barrel, bar-movement, lever watch, No. 36,175 (fitted with "Guillaume" balance), sent by Paul Ditisheim, La Chaux-de-Fonds. This obtained 96.1 marks, being 1.2 marks above the total obtained by a watch of the same maker in 1903, which has hitherto been the record at this Institution. In view of the transfer of all rating work to Teddington, this watch must remain the record for Kew.

The full records of the trial results were not usually published, but because Ditisheim's watch, No. 36,175 achieved the highest marks ever recorded at Kew, and in its final year of trials, the full rate sheet for the watch was published. This allows the method of calculating the Kew trial marks to be examined in detail and there is an analysis of these results at the end of this section.

The list of the top 50 watches from 1912 was not comfortable reading for English watch manufacturers. Victor Kullberg, London, came second with 93.1 marks; a creditable effort but not enough to beat Ditisheim, or Ditisheim's 1903 record of 94.9. Only three other English manufacturers made the cut; S Smith & Son at number 9, Robert Kunzler, Birmingham, at number 28 and E. Dent & Co., London, at number 38. All the other 46 places were taken by Swiss manufacturers apart from one, which was taken by the Waltham Watch Co., Waltham, Mass. Ditisheim had a second watch in the top 50 at number 12. The largest number of places was taken by Patek, Philippe & Co., Geneva, with 12 places, followed by Longines and Vacheron & Constantin, each with nine places, Golay, Fils & Stahl, Geneva, with 6 places, Stauffer Son & Co., London and Fabrique d’horlogerie Electa (Gallet & Co.) La Chaux-de-Fonds, each with with three places and Audemars Piguet & Co. with one place.

Decline of English Entries

Longines Advert about 1921 Kew Results
Longines Advert about 1921 Kew Results: Click image to enlarge

In an article in the AHS journal Antiquarian Horology, Mike Dryland analyses the performance of English and Swiss companies in the Kew watch trials. In the 22 years from 1885 to 1906, an English watch obtained the highest number of marks 16 times. English watches obtained the highest number of marks from 1897 to 1906, except for a watch entered by Paul Ditisheim in 1903. The last English watch to obtain the highest number of marks was in 1906 when a double roller fusee single overcoil tourbillon watch entered by Charles Frodsham achieved 93.9 marks.

The low point for Swiss watch was in 1902, but then Swiss entries started to displace English watches from the top places. By 1908, Swiss watches were dominating the top places, led by regular demonstrations of excellence from Patek Philippe and Vacheron & Constantin, and startling leaps forward by Paul Ditisheim.

After Ditisheim's success in 1903, Swiss entries increasing used the Guillaume compensation balance. This balance reduced the middle temperature error, which resulted in higher marks in the temperature compensation test. The Guillaume balance is sometimes identified in the Kew results quite incorrectly as an Invar balance, or an Integral or Crausaz balance. All these names refer to the same type of balance. Before 1913, Guillaume balances are reported a few times in the Kew results, it seems quite likely that its use was being under reported. However, in the trial results for the year from January 1913 to March 1914, suddenly almost every single watch is reported as having a Guillaume or Integral balance. This followed a letter by Guillaume that was published in the Journal Suisse d'Horlogerie in August 1912 where he pointed out the inconsistency of names used and lack of consistency in reporting the use of the balance. This appears to have woken up the Kew authorities to the significance of the Guillaume balance, after which it was reported more consistently.

The advertisement here by Longines records a very good results for them in the trials from 1 October 1920 to 30 September 1921. The text of the advert says "An unprecedented record in the history of chronometry! 20 Longines CHRONOMETERS were classified at Teddington Observatory IN A SINGLE AND SAME YEAR OF COMPETITION with a number of points greater than 90. It was also a LONGINES Chronometer which obtained the best ranking in the 1918-19 competition. All these chronometers were fitted with the GUILLAUME balance."

In fact, “only” 16 of the Longines chronometers obtained over 90 marks, the lowest scored of the 20 obtained 88.4 marks; still a pretty remarkable result. The watches were all double roller, going barrel, 2 day deck watches. They were all fitted with Guillaume balances.

Certificate Classes

Class A

The Class A trial was performed over 45 days divided into 8 periods of 5 days. The rate on the first day was not recorded, and a day was allowed between changes in temperature to allow the watch to stabilise at the new temperature. In each period the rate of the watch was checked 5 times every day.

Class A Trial Schedule
PeriodPositionTemperature
1Pendant up 67°F (room temperature)
2Pendant right67°F (room temperature)
3Pendant left 67°F (room temperature)
4Dial up 40°F (refrigerator cold)
5Dial up 67°F (room temperature)
6Dial up 83°F (oven heat)
7Dial down 67°F (room temperature)
8Pendant up 67°F (room temperature)

To pass the Class A trial, a rate of a watch had to meet the following conditions:

  1. The mean difference of daily rate, under the same conditions of position and temperature, had in no instance exceeded 2 seconds.
  2. The mean daily rate in a vertical position (pendant up/left/right) had differed from the mean daily rate in a horizontal position (dial up/down) by less than 5 seconds, and from that in any other position by less than 10 seconds.
  3. The mean daily rate had been affected by changes of temperature by less than one-third of a second per 1° Fahrenheit.
Assigning of Marks
Assigning of Marks: Click image to enlarge

It was initially intended that the trials would not be competitive and that all watches passing the Class A trial would awarded the same “pass” certificate, which is why there are no results from 1884. From 1885, marks out of 100 were awarded for watches that passed the trial, with a watch that only just passed being awarded 0 marks and a watch that exhibited no variation in rate being awarded 100 marks.

Note that, in common with the Greenwich trials of box chronometers, the rate did not have to be zero, it was the variation in rate that was important. The time given by a watch with a constant rate could be corrected, whereas the time given a watch with a rate that varied from day to day could not. Consequently, watches that exhibited the least variation in rate, whatever that rate was, would be awarded the highest marks.

The 100 marks were allocated as stated by G. M. Whipple in the letter reproduced here:

Note that the marking scheme meant that a Class A certificate could be awarded to a watch that achieved zero marks, although none such is currently known.

From 1885 to 1890 a Class A certificate was endorsed with “especially good” when the difference described in (1) had in no case exceeded 0.75 second, when the differences described in (2) were less than 2.5 and 5 seconds respectively, and when the alteration of rate described in (3) was less than 0.15 second per 1° F.

From 1890 the endorsement “especially good” was applied to any watch achieving 80 marks or more.

Class B

Stauffer advertisement January 1894.
Stauffer advertisement January 1894.: Click image to enlarge

The Class B trials were a quicker and slightly easier way for a good quality watch to get a Kew certificate.

Class B trials were conducted over 31 days in two positions, pendant up and dial up, and three temperatures, room, refrigerator and oven.

The maximum allowed variation in daily rate was 2 seconds in any one position, 10 seconds between horizontal and vertical positions and \( \frac{1}{3} \) of a second per degree Fahrenheit.

The London importers of Swiss watches Stauffer & Co not only scored highly in the Class A trials, but also entered very large numbers of watches for the Class B trials. The fact that they could do this on a commercial basis, rather than entering just one or two very specially adjusted watches, shows that their ordinary watches were very good quality.

The advertisement reproduced here shows the large number of watches that Stauffer entered for the Kew trials in 1892, over half the total number entered. Although some of these were entered for Class A, many were entered for the Class B trial.

Class C

Class C trials were conducted over 16 days at room temperature only and two positions, eight days pendant up and eight days dial up. The maximum allowed variation in daily rate was 2 seconds in any position and 10 seconds between two positions.

Class C trials were discontinued in 1897 due to lack of demand.

Reissued Certificates

Stauffer letter to Dr. Chree at Kew
Stauffer letter to Dr. Chree at Kew: Click image to enlarge

The letter shown here is dated June 4th 1897 and addressed to Dr Charles Chree at the Kew Observatory, Richmond. Dr Charles Chree F.R.S. (1860-1928) was Superintendent of the Kew Observatory at Richmond in Surrey, England, from 1893 to 1925, a remarkably long service of 32 years.

The letter asks Chree if he will exchange an enclosed certificate for “one made out in a gold case”, explaining “we omitted to alter the original certificate before sending it in for transfer.” The certificate in question would be a Kew Certificates awarded to a watch that successfully passed the Kew trials.

Kew certificates were highly regarded and watch manufacturers would request Kew to reissue them in the name of a retailer or the final purchaser of a watch. In this instance, the watch was submitted for trial in a less expensive, probably silver, case which has been changed to a gold case before the watch was sold to a retailer. The original certificate had been altered to reflect either the retailer's or final customer's name, but the change of case material had not been noted.

Calculating Trial Marks

In the final year of watch trials at Kew, before the work was transferred to the National Physical Laboratory at Teddington, a watch submitted by Paul Ditisheim, No. 36,175, achieved the highest marks ever recorded at Kew. As a consequence of this, the full rate sheet for the watch was published. This allows the method of calculating the Kew trial marks to be examined in detail.

The summary of the result for Ditisheim watch No. 36,175, published in the report of the top 50 watches which obtained the highest number of marks at Kew during the year 1912, is reproduced below.

Summary of Ditisheim record established at Kew in 1912
Summary of Ditisheim record established at Kew in 1912: Click image to enlarge

Marks were awarded for performance under three headings: daily variation of rate (0 - 40 marks), change of rate with change of position (0 - 40 marks) and temperature compensation (0 - 20 marks). The four columns to the right hand side of the table give the marks for each category and the sum total of marks.

Between the columns for Mean Daily Rate and the columns of marks are three columns headed “Mean daily variation of rate Unit 0.01 second”, “Mean change of rate for 1°F Unit 0.001” and “Difference between extreme gaining and losing rates”.

The calculation of marks for temperature compensation is straightforward from the result quoted in the summary, but the marks awarded for daily variation of rate and change of rate with change of position cannot be calculated from the data given.

The marks awarded for temperature compensation are calculated as follows. A watch that had a variation of mean daily rate of one-third of a second per 1°F change of temperature would be awarded no marks, the marks rising to 20 for a watch that had no variation in rate with change of temperature, that is, one with perfect temperature compensation.

The column headed “Mean change of rate for 1°F Unit 0.001” contains the number 5, that is a variation of 0.005 seconds per day per change of temperature of 1°F. This is converted into marks by multiplying 20 by the ratio of 0.005 to one third, remembering that increasing marks are awarded the smaller the ratio: 20 × ( 1- 0.005/0.3333) = 19.69, which would be rounded to 19.7. The figure actually given in the table is 19.6, probably due to rounding in the hand-made calculations at the time.

The daily variation of rate is defined as the daily variation of rate from the mean rate for the period. During each five day period, watches were rated at the same time each day by comparing their rate to the observatory standard clock. For each five day period, the mean rate was calculated from the daily rates, and then the mean variation of the daily rates from this mean rate. The mean rates in positions are quoted in the summary, but not the mean daily variations from these. The figure of 13 given in the column headed “Mean daily variation of rate Unit 0.01 second”, that is 0.13 seconds per day, has to be taken at face value.

The change of rate with change of position was calculated from the mean rates for six of the eight periods, excluding the periods in the refrigerator and oven to eliminate variations due to temperature. An overall or “grand” mean rate was calculated from the mean rates for each period, and then the mean deviation of the period rates from this overall mean rate.

The column headed “Difference between extreme gaining and losing rates” is something of an anomaly. This difference was not used in the calculation of marks and it is difficult to see why it was tabulated at all. For the Ditisheim watch that took the Kew record in 1912, it is the difference between the maximum gaining rate on day 17, +1.5 seconds per day, and the maximum “losing” rate of day 41, which was actually a gaining rate of 0.25 seconds per day, giving a difference of 1.25 seconds per day.

Analysis of Results for Ditisheim watch No. 36,175

The rate sheet for Ditisheim watch No. 36,175 at Kew during the year 1912 is reproduced below.

Rate sheet for Ditisheim watch No. 36,175 at Kew in 1912
Rate sheet for Ditisheim watch No. 36,175 at Kew in 1912: Click image to enlarge

The tables below show how the calculations were performed. The Roman numerals show the period, the following letters show the position: PU pendant up, PR pendant right, PL pendant left, DU dial up, DU dial down. The blue and red colours show the periods of cold and heat.

The calculation of marks for daily rates included all periods. The measurements of rate, and calculation of marks, for temperature compensation were conducted all with the dial up, to eliminate variations due to changes in position. The calculation of marks for position excluded the periods of cold and heat, to eliminate variations due to temperature.

Constancy of Daily Rate







Period I PU II PR III PL IV DU V DU VI DU VII DD VIII PU
Average departure of daily rate from mean rate for period (second per day) 0.16 0.20 0.12 0.10 0.20 0.12 0.00 0.16
Grand mean variation of daily rate 0.13









Constancy of Rate with Change of Position







Period I PU II PR III PL V DU VII DD VIII PU

Mean rate for period (second per day) 0.80 0.75 0.65 1.00 1.25 0.55

Grand Mean 0.83

Variation of mean rates from Grand Mean (second per day) 0.03 0.08 0.18 0.17 0.42 0.28

Mean variation of rate with change of position 0.19










Constancy of Rate with Change of Temperature








Rate (sec per day). Temperature (°F).

Period IV V VI IV V VI

Mean rate and temperature 1.25 1.00 1.10 40.00 65.00 90.00

Grand Mean 1.12 65.00

Departure from Grand Mean 0.13 0.12 0.02 25.00 0.00 25.00

Sum of departures 0.27 50.00

Mean change of rate per 1°F change of temperature 0.005

The marks for each category are calculated from these results as follows:

Constancy of daily rate. Zero marks for 2 seconds to 40 marks for no variation: \( 40 \times ( 1 - \frac{0.13}{2} ) = 37.4 \)

Constancy of rate with position. Zero marks for 10 seconds to 40 marks for no variation: \( 40 \times ( 1 - \frac{0.19}{10} ) = 39.2 \)

Constancy of rate with temperature. Zero marks for \( \frac{1}{3} \) second to 20 marks for no variation: \( 20 \times ( 1 - \frac{0.005}{\frac{1}{3}} ) = 19.7 \)

Total marks: 37.4 + 39.2 + 19.7 = 96.3

The individual marks calculated here differ slightly from the published Kew results, giving an extra tenth of a mark for constancy of rate and temperature compensation. This is probably due to rounding in the original hand-made calculations.

Tourbillons and Karrusels

The Tourbillon was invented by Abraham Louis Breguet, who was granted a patent for the invention in 1801. It is a cage which contains the escapement, balance and spring, rotating them so that errors of poise are evened out over time. The Karrusel is a similar mechanism, but more robust and slower rotating, invented in 1892 by Bahne Bonniksen, a Danish-born watchmaker working in Coventry.

A Tourbillon or Karrusel evens out over time errors of poise in the balance and associated components, the balance spring and collet. An error of poise means that the the balance, spring and collet have a heavy point. When the watch is in the vertical position, this heavy point causes the watch to go faster or slower depending on the amplitude and the vertical orientation of the watch. Tourbillons and Karrusels are only effective in the vertical positions, because in the horizontal positions gravity makes no contribution to the turning forces acting on the balance.

Large numbers of watches with Karrusels were entered for the Kew trials by English watchmakers between 1894 and the First World War. However, Karrusel watches were not as successful in the Kew trials as is sometimes claimed. A Karrusel watch came first in the results only five times over the period of twenty years, and none of them established a new record. Only one of these five Karrusel watches, one entered by Victor Kullberg in 1905, achieved a better result than the 91.9 marks of the 1892 Baume watch, with 92.7 marks. By this time though, the record was held by a Ditisheim watch entered in 1903 which was awarded 94.9 marks.

It is sometimes thought that a revolving escapement such as a Tourbillon or Karrusel was needed to achieve high marks in observatory trials such as those held at Kew. However, analysis of results from the Kew trials shows that the benefit to a well-adjusted watch of a revolving escapement against a fixed escapement is not significant. Over the 41 years between 1885 and 1926, watches with revolving escapements of either type achieved the highest number of marks 15 times, against 26 times for watches with fixed escapements.

It is true that the Tourbillon watches of Stauffer, Son & Co, in 1891, and Baume in 1892, held the Kew record until 1902 when a watch by H. Golay, also with a Tourbillon, established a new record, followed by another new record in 1903 set by a Tourbillon watch by Paul Ditisheim. However, when considered over the 41 years between 1885 and 1926, the performance of Tourbillon and Karrusel watches does not stand out saliently against watches with fixed escapements.

As an example, in 1911, of the 50 watches that obtained the highest number of marks, all of which achieved more than 86 marks, only six had revolving escapements. Two watches with fixed escapements entered by Paul Ditisheim received the highest number of marks, 94.8 and 93.1 out of a possible 100. The highest-placed watch with a revolving escapement was thirteenth, the other five were ranked thirty-seventh and lower. Evidently, a Tourbillon or Karrusel was not necessary to achieve high marks and was also not a guarantee of success.

Reducing Poise Errors

Watchmakers poise a balance using a poising tool with knife edges on which the balance staff is rested. An out of poise balance will rotate and move along the knife edges until its heavy point is down. Material is then added or removed at the appropriate points until the balance does not move when it is placed on the knife edges. This is called “static poising” and it is of little benefit. Balances that are statically poised and then fitted with a collet and balance spring and poised in a running watch are out of poise if they are subsequently tried on the knife edges.

Adjusting poise errors in a running watch is called dynamic posing. The rate of the watch is measured in four or more vertical positions and the location of a heavy spot noted. Material is then added or removed at the appropriate points on the balance until the rate is the same, or as close as can be reasonably obtained, in all the vertical positions. In the days before electronic watch rate machines were available, this work took a skilled adjuster many hours or days to perform, because each measurement of rate in the vertical positions required that the watch be run for several hours before its rate against a regulator, usually an accurate pendulum clock, could be recorded.

A watch with a Tourbillon or Karrusel cannot be dynamically poised. This means that the oscillator assembly will inevitably be out of poise, no matter how well the balance has been statically poised. The Kew trial results show that a Tourbillon or Karrusel does not cause an improvement of the performance in vertical positions compared with a watch that has been dynamically poised.

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Copyright © David Boettcher 2005 - 2024 all rights reserved. This page updated February 2024. W3CMVS. Back to the top of the page.