Abstract: The invention is directed to an angle-measuring instrument such as a theodolite, tacheometer or the like having a coarse-fine drive arrangement for presetting a circle part of a graduated circle to a predetermined read-out value. In a preferred embodiment, a coaxial coarse-fine drive arrangement is actuated by a single control knob which is part of an adjustable drive which can be operated in two positions. In the first position, the adjustable drive functions as a coarse drive and includes a spur gear that meshes with a gear on the carrier of the graduated circle to permit adjusting the circle part to obtain a coarse setting thereof. When the control knob and adjustable drive are moved into the second position, the drive becomes completely disengaged from the carrier and functions as a fine drive that operates on a plane-parallel plate pivotally mounted in the read-out optical transmission path of the instrument to finely adjust the light rays passing therealong.

Abstract: The invention contemplates a method of calibration (FIG. 1) for determining the distance (base length E.sub.b) between two angle-measuring instruments (theodolites 1, 2) used for triangulating measurement of coordinates of given points on larger objects.For this purpose, a horizontal measurement bar (3) is fixedly set up between the measuring instruments (1, 2). The bar mounts at least three spaced target marks (4, 5, 6) in the form of balls which can be sighted from both sides, i.e., by both angle-measuring instruments (1, 2). The base length is calculated from the predetermined distance between the marks (4, 5, 6), and from difference in angles measured for each sighting.Precise alignment of the bar (3) is not necessary, since inclination of the bar to the line connecting the theodolites can be calculated from the measured angles, for sightings made upon different pairs of marks (4/5 and 5/6, respectively).

Abstract: The invention contemplates a target device for marking inaccessible measuring points on industrial objects such as, for example, an airplane fuselage which is to be measured for coordinates of certain points on its surface, using a pair of theodolites.The target device consists of a rod-shaped holder (1) on which two spherical target marks (4, 5) are so arranged that the measurement point lies on the extension of the line connecting the target marks, and at known offset from the measurement point.For attachment to the object (12) to be measured, the holder (1) employs removable adapters, such as threaded bolts (3).