'I Expect that some of us are unaware of the significance of the name "Tavistock Theodolite"; so I had better make it clear at the outset that the name applies to certain theodolites that are now being produced to a specification drawn up as the result of a meeting of British instrument makers and surveyors at Tavistock in 1926.'¹ This is how an article from 1929 by E.R.L. Peake starts describing this instrument.

Peake continued:

As a result of this meeting a specification for a British theodolite was drawn up, as we were all convinced that an all-British instrument could be produced that would combine the latest ideas in design with the well-known qualities of strength and reliability possessed by the existing types of British make. The chief difficulty the makers had to contend with was in producing an instrument that would not transgress existing patents. Messrs. Cooke, Troughton & Simms, Ltd., have succeeded in doing this, the optical arrangements of their model and the method of reading it being different in every respect from existing patterns. Messrs. E. R. Watts & Son, Ltd., on the other hand, came to an agreement with the firm of Zeiss and have incorporated in their model several of the Zeiss patents; thus it can hardly be said that theirs is an all-British instrument. So far nothing has materialized from the third firm of instrument makers, Messrs. C. F. Casella & Co., Ltd...'

According to Peake the Cooke, Troughton & Simms prototype for the Tavistock was a '...3½ inch Double-Reading Theodolite. The horizontal circle is 3½ inches in diameter and is flat divided on glass to 20'; the vertical circle is 2¾ inches in diameter and similarly divided.

Above description fits the original prototype presented in 1929, But the '...method of reading [of the circle] has not received universal approval, and the makers are now at work on a second model, which, though built on the same general lines as the earlier one, incorporates a method of reading invented and patented by Captain T. Y. Baker, b.a., r.n., which is very ingenious.'¹ Baker's method however needed a complete redesign of the reading microscopes and thus resulted in a complete new instrument, the one shown here, and which was launched in 1931.⁴

The circles remained the same as in above described prototype. Thanks to Baker's new circle reading method the circles can now be read directly to 1 arc second and estimated to tenths of an arc second (see figure 26 and figure 27).⁵

The plate vial on the horizontal circle of the instrument shown here (see figure 6) has a sensitivity of 40 arc seconds per 2 millimetres run as described in the Cooke, Troughton & Simms CV400A brochure,⁵ while another Tavistock that I have seen, that was despatched in 1945 (two years after the one shown here), was equipped with a 30 arc second per 2 millimetres run plate vial.

The coincidence vial has a sensitivity of 23 arc seconds per 0.1 inch (see figure 14) as indicated in the brochure,⁵ while at the 1945 version this had been increased slightly to 20 arc seconds per 0.1 inch.

It seems that Cooke, Troughton & Simms was experimenting with these parts ever since they designed the instrument.

With serial no. 41274 the Tavistock shown here dates from August 1943. It was part of a large order of 228 Tavistock Theodolites with tripods T95 despatched to the Ministry of Supply (Contracts Dept.), Great Westminster House, Horseferry Rd., Westminster SW1 on 5/8/1943.⁶

When the ministry was set up under the Ministry of Supply Act 1939 it became responsible for the administration of the Royal Ordnance Factories and for design, inspection, research and experimental work in connection with the supply of munitions, clothing and other stores to the War Office and Air Ministry. It was also responsible for the supply of certain common stores to the Admiralty, Ministry of Home Security, Office of Works and subsequently to other government departments.⁷

How it ended up in the United States is still unclear, but it may have been sold during one of the sales of R.A.F. surplus stores in 1949.⁸

The instrument is remarkably complete and came with its original metal case (see figure 18 and figure 19) which can be carried as a rugsack (see figure 20). When it arrived it was in a sorrow state with broken and bend knobs and a lot of friction in the primary and secondary axis and the scale microscopes. All parts were however in the box, while cleaning and lubricating a Tavistock is relatively easy when compared to the Wild instruments. It took about a whole day to get the instrument back into working order again and now stands proud next to the instruments that it originated from (see figure 4).