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

Escutia crouched down in front of his alidade - an age-old, compass-based device - and sighted the fire: 152 degrees, southwest.

From BBC • Aug. 15, 2022

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

From Economist • Oct. 26, 2017

The alidade is a triangular ruler with one or more working scales on it beside other measurements.

From Military Instructors Manual by Schoonmaker, Oliver

The second lesson takes up the preparation of the stride scale on the alidade and the different kinds of maps, made in military sketching.

From Military Instructors Manual by Schoonmaker, Oliver

Surveying Compass, about 1780, made of brass, overall length 13-3/4 in., diameter of dial 5-1/4 in., silvered bubble level, vernier on alidade.

From Early American Scientific Instruments and Their Makers by Bedini, Silvio A.