level: name for different types of instrument used in surveying for determining the horizontal direction and differences in height, and in gunnery and elsewhere for adjusting something to the horizontal. See also gunner's level.
level and sight: instrument used to set a large gun to the horizontal, or to elevate and aim it on a target, see article on the gunner's sight and level.
limb: the outermost part or edge of a circular or part-circular instrument carrying a scale, usually divided in degrees.
