ALIDADE (from the Arab.), the movable index of a graduated arc, used in the measurement of angles.
THEODOLITE,' a surveying instrument consisting of two graduated circles placed at right angles to each other, for the measurement of horizontal and vertical angles, a telescope, which turns on axes mounted centrically to the circles, and an alidade for each circle, which carries two or more verniers.
Crossed out, the circle being crossed by diameters to show the degrees; others have found in it a corruption of "the alidade" (q.v.).