A well-logging device which photographically records the borehole [[azimuth]] and [[deviation]] from the vertical.
In the [[cartridge]] of the downhole instrument. a compass needle indicates magnetic north and a steel ball rolling freely on a graduated concave glass indicates the hole [[deviation]]. A lens focuses these images on photographic film which is exposed, frame by frame, when the [[tool]] is held motionless, centered in the borehole at preselected stations. Compare [[poteclinometer]].