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Theodolites have been used to measure horizontal and vertical angles by surveyors since the 1500s. A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are used mainly for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology. Theodolites, such as this one, were instrumental to early surveyors, and would have played a significant part in their everyday work. The plumb bob was used to set the instrument exactly over a fixed survey marker.This theodolite was made by Troughton and Simms, who were significant scientific instrument makers of the 19th century and early 20th century. In 1782 John Troughton purchased Benjamin Cole's shop in Fleet Street, London enabling him to sell his own signed products. His instrument making business supported several dynasties of Troughtons before becoming Troughton and Simms and later still Cooke Troughton & Simms. This firm was one of the most well respected firms of instrument makers of the 1800s. A grey metal theodolite - probably made of brass. It has movable parts and there is a weight ( a plumb bob) attached with string.Cooke Troughton & Simms Yorke England V012318 Supplied by A. E. Parsons Melbournetheodolite scientific-instruments surveying