goniometres

A goniometer is an instrument for measuring angles or the orientation of an object. The name derives from Greek gonia, angle, and metron, measure. Goniometers vary from simple two-arm protractors to complex rotation stages and are used across disciplines to measure planar angles or spatial orientations.

In geometry, surveying, and physical therapy, a common form is the universal or mechanical goniometer: two arms joined at a hinge with a graduated scale. The arms align with the rays of the angle, and the scale reading provides the angle. Some clinical goniometers feature digital readouts or fixed anatomical landmarks for standardized joint measurements.

In crystallography and materials science, a goniometer is a precision rotation stage that positions a crystal relative to an X-ray beam or detector. It can rotate about one or more axes with fine angular resolution, enabling measurement of diffraction angles and crystal orientation.

Digital and electronic variants use sensors, inclinometers, or optical encoders to provide continuous angle readouts and are often integrated with imaging, motion capture, or CAD workflows. Goniometry is used in fields ranging from medicine and engineering to science and aesthetics, reflecting the broad utility of accurately measuring angles.