Abstract: An optical system of a theodolite has an altitude angle scale plate having an altitude scale, a horizontal angle scale plate having a horizontal angle scale, a light path combining member for combining the light paths from the two scale plates, a rectangular prism member provided between one of the two scale plates and the light path combining member and having slant faces orthogonal to each other, the light beam from said one of the two scale plates being reflected by the inner surfaces of the orthogonal slant faces of the rectangular prism and thereafter reaching the light path combining member, an objective lens disposed at the exit side of the light path combining member to form the images of the scales on the two scale plates and a focusing screen on which the images of the scales by the objective lens are formed.

Abstract: The invention relates to an arrangement for determining the vertical axis of a surveying device including a horizontal and a vertical circle each being provided with an index. The two indexes are related to each other and the resulting departure, if any, is measured either visually or physically. By virtue of the inventional arrangement additional means for determining the vertical axis of a surveying device such as inclinometers are eliminated.

Abstract: A light emitting diode is located beneath a glass scale carrier, one for each scale (azimuth and elevation), emitting essentially monochromatic light, which penetrates through the glass scale; the scale is observed through an optical system. The optical system for viewing of the scale is located on a carrier secured in the telescope housing; the light emitting diodes are powered by a battery secured in the housing, which energizes a timer, such as R/C circuit settable for normal observation times, for example about thirty seconds.