The DKM2 is a double-circle theodolite with an optical micrometer. Heinrich Wild developed the form for Kern in the 1930s. Like the T2 manufactured by Wild in Heerbrugg, the DKM2 is a lightweight instrument with a steel frame. The horizontal and vertical circles are glass, and read directly to single seconds. The telescope is equipped with stadia wires, and so can be used for tachymetry. An auxiliary eyepiece lying alongside the telescope allows the user to read either circle without moving away from the station. Here, however, the two scales are read through the optical micrometer with reference to a centrally located index, giving the arithmetic mean of two diametrically opposed points on the circle. In 1955, an instrument of this sort, with tripod, cost $1,221. This example is marked "Kern AARAU SUISSE SWITZERLAND No 37845 DKM2." It was purchased in 1963, and given to the Smithsonian in 1997.
Ref: Kern & Co., Ltd, Double Circle Theodolites (about 1959).
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