Triquetrum(redirected from triquetral bone)
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an ancient astronomical goniometric instrument that was used to measure the zenith distances of celestial bodies. The triquetrum consisted of two hinged rods and a vertical post, which together formed an isosceles triangle whose vertex angle could be varied according to the zenith distance being measured. The length of the rod located at the base of the triangle was used as the measure of the angle. The triquetrum was used in astronomical observations as late as the 16th century by, for example, Copernicus.