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Ramsden Theodolite The evolution of the theodolite began with the description of the instrument included within the book Pantometria, by Leonard Diggs in 1571. After two centuries of adaptations and improvements, the theodolite reached a final basic form in the late 18th century. It was during this time period that a very unique theodolite was built. In 1775 Jesse Ramsden completed his circular dividing engine. This engine enabled much more accurate divisions than the previous laborious and tedious means of manually dividing circles. In the year 1782, it was proposed by British cartographers that the relative locations of both the Royal Observatory in Greenwich England and the Observatory in Paris France, be tied together by means of triangulation, and then the whole of Britain be divided into great triangles. Ramsden Theodolite model Ramsden Theodolite drawing Jesse Ramsden was appointed to build a theodolite that was capable of the accuracy required for such surveys. And so, in approximately 1782 Jesse Ramsden commenced construction on his Great Theodolite. The instrument when completed, (a three year project), incorporated a 3 foot diameter horizontal circle and weighed approximately 200 pounds. It was used by General Roy for locating the Greenwich and Paris observatories as well as the Ordinance Survey of Great Britain. The Great Theodolite continued being used for important surveys and is now housed in the Greenwich Museum in England. Jesse Ramsden was London's leading maker of astronomical instruments