alidade

American  

[al-i-deyd] / ˈæl ɪˌdeɪd /

Also alidad

noun

Surveying.

1. (in plane-tabling) a straightedge having a telescopic sight or other means of sighting parallel to the straightedge.

2. the entire upper part of a theodolite or transit, including the telescope, its supports, the level vials, the circle-reading device, and the spindle.

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alidade British  

/ ˈælɪˌdæd, ˈælɪˌdeɪd /

noun

1. a surveying instrument used in plane-tabling for drawing lines of sight on a distant object and taking angular measurements

2. the upper rotatable part of a theodolite, including the telescope and its attachments

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Etymology

Origin of alidade

1400–50; variant of alhidade < Medieval Latin alhidada < Arabic al-ʿiḍādah the turning radius (like a clock hand) of a circle; replacing late Middle English allydatha (< Old Spanish alhidada )

Example Sentences

Mr. Dalton showed the couple around the lookout, explaining the old telephone system and the fire finder, a type of alidade used by fire lookouts.

From New York Times

The complete instrument would also have had a rotating pointer, called an alidade, mounted on a pin running through the central hole.

From Economist

An additional article of the sketcher's equipment is a holder for his pencils, alidade, eraser, knife, pins, etc.

From Project Gutenberg

Problem.—By use of the slope scale on the sketch board and the contour interval scale on the alidade, each man will secure vertical data on the flat sketch made in the fourth lesson.

From Project Gutenberg

It consists of a frame in the form of an octant having a graduated scale upon its arc, and an index arm, or alidade pivoted at its apex.

From Project Gutenberg