Theodolites are a surveying instrument used for measuring horizontal and vertical angles. Theodolites use a telescope mounted within two perpendicular axis, horizontal and vertical where angles can be read from. Conventional theodolites do not require electricity to operate, except for when they are mounted with an EDM (electronic distance measure). They have been used for centuries, and although total stations are the main tool of use in the modern era, they make use of an electronic theodolite. Older theodolites may still be used in certain mines, particularly in gassy coal mines which have been determined unsafe for the use of electronic equipment in certain sections of the mine (where there is risk of explosions). It should be noted however, that with the use of intrinsically safe total stations (e.g. modified Leica TPS400); older theodolites are becoming a tool of the past, commonly used as a teaching aid for showing students where modern instruments derived.
Note: Intrinsically safe refers to equipment/wiring which will not release enough electrical or thermal energy to cause ignition of a hazardous atmospheric mixture.
Theodolites (albeit have changed over time) were first evident in the late 1500's. Prior to theodolites, Dioptras were used. Modern theodolites were first introduced in 1787, and were progressively updated for different uses and with different mountings. They were used in the 1870s by the U.S. Navy to obtain the first precision surveys of American harbours.
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