Optical square

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a surveyor's instrument with reflectors for laying off right angles.

See also: Optic

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Trombettoni, "Topological phase transitions driven by non-Abelian gauge potentials in optical square lattices," Physical Review A: Atomic, Molecular and Optical Physics, vol.
angle measurement,2.Linear distance measurement,3.Vertical (distance) measurement.Angle measurement tool of early Egyptians Groma was basically similar to optical square for right angles setting out.
--Acquaintance with the optical theodolite, levelling instrument, optical square and laser level.
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