The aiming circle is basically a telescope mounted on a base which permits exact azimuth and elevation measurements. The main housing is placed in a true level condition by two types of levels: the circular level is used for coarse leveling & the tube levels are used for fine leveling
A tube level on the elbow telescope permits the elbow telescope to be adjusted to a true horizontal line of sight. A magnetic compass is located in an oblong box on the top of the main housing.The magnetic compass needle can be seen through a window or through the magnifier.
Zero azimuth heading with respect to magnetic north or any other selected compass heading can be made by turning the orienting knobs or the azimuth knob. Elevation angle of the telescope is adjusted by turning the elevation knob .
Azimuth and elevation angles up to 85 mils can be read from the horizontal and vertical centerline on the reticle while looking through the elbow telescope.
See here the Dutch description
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