BO in short. Richmond's intention was to use the new theodolite on the extension of Roy's survey to the southern counties of Britain. The instrument was basically the same as the first with added refinements, mainly to the number and placement of the microscopes with their precision micrometer stages. It was in use until the completion of the Principal Triangulation of Great Britain in 1853 and it is now in the Science Museum in London. There is a description of the improvements made to this theodolite in the account of the Trigonometrical Survey for the years 1791–1794 by Mudge, Williams and Dalby. Other Ramsden theodolites Ramsden made at least one other theodolite of which parts were discovered in Switzerland. After his death his firm was inherited by Mathew Berge who is known to have constructed two more large instruments to Ramsden's design. Ramsden made many theodolites including an eighteen-inch instrument of the same general design as the great theodolites. This instrument and his two great theodolites are described in the account of the Principal Triangulation by . Great theodolites by other builders Although the East India company turned down Ramsden's second theodolite they commissioned a similar design from another London instrument maker, William Cary. This theodolite was in use in India from 1802 although there was a slight hiatus in 1808 when it was damaged when being hauled to the top of a building. It was repaired and in use for sixty years. A new theodolite to an improved design was made for the Indian Survey by Troughton and Simms in 1830 and the two together saw service until 1874 when the Cary instrument was replaced by another by Troughton and Sims. This last instrument was a monster weighing when in its travelling cases: it was no surprise that it was deemed too heavy for transport up mountains and it passed to South Africa in 1882. No more great instruments were made after 1874 for continuing advances in precision instruments eclipsed their performance: by the end of the nineteenth century an accuracy of 1 arc second could be obtained with a instrument. Chains and rods Eighteenth-century surveyors used Gunter's chains which were 22 yards long (one chain with 100 links of 7.92 inches). Their accuracy was adequate for cadastral surveying but they were deemed insufficiently accurate for the Anglo-French Survey (1784–1790), Britain's first high-precision survey. Roy asked Ramsden to prepare