Triquetrum (astronomy)
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Drawing of a triquetrum by Wilhelm Schickard, Basel University Library
A triquetrum, or three-staff, is an ancient astronomical instrument developed by Ptolemy in the 2nd century A.D. Consisting of two intersecting arms hinged to a vertical post, the triquetrum enabled calculation of the angular elevation of a heavenly body observed through a sight mounted on the upper arm.
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