A sighting device or pointer for determining directions or measuring angles, used in surveying and (formerly) astronomy.
- A pointer, called an alidade, was pivoted at the centre of the disk.
- A wide variety of alidades and plane tables are available, both in manual and electronic versions.
- In the circle an index on the alidades gives the angle that they form with the vertical diameter.
Late Middle English: directly or (in modern use) via French and Spanish from Arabic al-‘iḍāda 'the revolving radius', probably based on aḍud 'upper arm'.
Definition of alidade in:
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