242,631. Goerz Optische Anstalt Akt.-Ges., C. P. Nov. 6, 1924, [Convention date]. Range-finders. - Range-finders utilizing the height above sea-level or the height of the target as a base, comprise a sighting telescope 17 adapted to be trained and elevated and supported in the vertical plane by a rotatable cam 7, the radii of which are exponential functions of the angles of rotation of the cam, so that the inclinations of the telescope may be read off directly as ranges on a logarithmic circular scale. An additional cam 8 provided on the same axle 6, whereby a correction is added on account of the curvature) of the earth's surface and the refraction of the air. In determining a range the cam 8 is first rotated by the worm 11 mounted on the cam 7 to adjust the position of the axle 6 for the corrections above mentioned and then the cam 7 is rotated by the axle 6 until the target is sighted in the telescope 17. The range is then read off the circular scale mounted on the axle 6 against a pointer fixed on the arm 5. The range scale, being logarithmic, may be set with the upper mark of the pointer 7a to indicate the height of the instrument, and thus enable the range to be determined at any height of the instrument. When utilizing the height of the target the range scale is set to the lower of the marks on the pointer 7<a> and an adjustable prism and reflector device, Fig. 6, is placed in front of one half of the objective, so that a double image is produced. One of the reflectors 25 is rotatable and the variable prism consists of two lenses 22, 23 the contacting surface having a radius equal to the distance from the pivot 4. The telescope is adjusted by the cam until the lower point of the target in the eyepiece can be brought into coincidence with the upper end by rotating the mirror 25. Mathematical formulae on which the invention is based are set out in the Specification.