Instrument, or part of an instrument , for determining direction , either horizontal or vertical In its simplest form, a peepsight or telescope mounted on a straightedge and used for plotting directions graphically In such instruments as transits and theodolites, the alidade is the part containing the telescope and its attachments
1 A sighting device used to locate points in the field from which the survey drawing is plotted 2 The index of an astrolabe, quadrant or other graduated instrument, carrying the sights or telescope, and showing the degrees cut off on the arc of the instrument
A stationary instrument, mounted on a stand, that measures the angle subtended at the stand by the horizon and an object in space The clinometer is a portable form of alidade frequently used with a ceiling projector to determine the height of clouds An alidade usually measures the elevation angle only; a theodolite measures azimuth as well
That part of a surveying instrument which consists of a sighting device and index, with accessories for reading and recording data A telescopic alidade is part of a theodolite or surveyor's transit, and when mounted on a straightedge, in conjunction with a plane-table, is used in topographic surveying (See theodolite and transit)
The portion of a graduated instrument, as a quadrant or astrolabe, carrying the sights or telescope, and showing the degrees cut off on the arc of the instrument surveying instrument used with a plane table for drawing lines of sight on a distant object and for measuring angles surveying instrument consisting of the upper movable part of a theodolite including the telescope and its attachments