A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry derives from two Greek words, γωνία (gōnía) angle and μέτρον (métron) measure. The protractor is a commonly used type in the fields of mechanics, engineering, and geometry.
The first known description of a goniometer, based on the astrolabe, was by Gemma Frisius in 1538.