Goniometer

A goniometer is an instrument that either measures angles or allows an object to be rotated to a precise angular position. The term goniometry is derived from two Greek words, gonia, meaning angle and metron, meaning measure.

Types
There are many types of goniometers, each specialised for its particular application.

Audio
An audio goniometer is used to visualize the amount of stereo in a signal.

Communications
Goniometers are used for direction finding in signals intelligence applications for military and civil purposes, e.g. interception of satellite and naval communications as performed on the French warship Dupuy de Lôme uses multiple goniometers.

Crystallography
in crystallography, goniometers are used for measuring angles between crystal faces. They are also used in X-ray diffraction to rotate the samples. The groundbreaking investigations of physicist Max von Laue and cohorts into the atomic structure of crystals in 1912 involved a goniometer.

Physical therapy
In occupational therapy and physical therapy, a goniometer is a tool which measures a joint's axis and range of motion. If a patient or client is suffering from decreased range of motion in a joint (i.e. a knee or elbow), the therapist can use a goniometer to assess what the range of motion is prior to intervention, and then make sure the intervention is working by using the goniometer in subsequent interventions.

Thermodynamics
In thermodynamics, the goniometer is used to measure the contact angle at which a liquid/vapor interface meets a solid surface. This application was invented by Dr. William Zisman of the United States Naval Research Laboratory in Washington, DC. These tools are used not only for contact angle and surface energy applications, but also to measure surface tension using pendant drop, sessile drop, and other techniques. The original manual contact angle goniometer used an eyepiece with microscope. The current generation of contact angle instruments uses cameras and software to capture and analyze the drop shape.

Positioning
A positioning goniometer or goniometric stage is a device used to rotate an object precisely about a fixed axis in space. It is similar to a linear stage, however, rather than moving linearly with respect to its base, the stage platform rotates partially about a fixed axis above the mounting surface of the platform. Positioning goniometers typically use a worm drive with a partial worm wheel fixed to the underside of the stage platform meshing with a worm in the base. The worm may be rotated manually or by a motor as in automated positioning systems.