Goniometer

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 is derived from two Greek words, gōnia, meaning angle, and metron, meaning measure. 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 is derived from two Greek words, gōnia, meaning angle, and metron, meaning measure. The first description of a goniometer, derived from the astrolabe, was apparently in 1538, by Gemma Frisius. Prior to the invention of the theodolite, the goniometer was used in surveying. The application of triangulation to geodesy was described in the second (1533) edition of Cosmograficus liber by Petri Appiani as a 16-page appendix by Frisius entitled Libellus de locorum describendorum ratione. The Bellini–Tosi direction finder was a type of radio direction finder that was widely used from World War I to World War II. It used the signals from two crossed antennas, or four individual antennas simulating two crossed ones, to re-create the radio signal in a small area between two loops of wire. The operator could then measure the angle to the target radio source by performing direction finding within this small area. The advantage to the Bellini–Tosi system is that the antennas do not move, allowing them to be built at any required size. The basic technique remains in use, although the equipment has changed dramatically. Goniometers are widely used for military and civil purposes, e.g. interception of satellite and naval communications on the French warship Dupuy de Lôme uses multiple goniometers. 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 colleagues into the atomic structure of crystals in 1912 involved a goniometer. Goniophotometers measure the spatial distribution of light visible to the human eye at a specific angular position. A goniometer is used to document initial and subsequent range of motion, at the visits for occupational injuries, and by disability evaluators to determine a permanent disability. This is to evaluate progress, and also for medico-legal purposes. It is a tool to evaluate Waddell's signs (findings that may indicate symptom magnification.) In physical therapy, occupational therapy and athletic training, a goniometer is an instrument which measures range of motion joint angles of the body. This measurement instrument is a helpful, clinical tool that allows for objective measurements in order to accurately track progress in a rehabilitation program. When a patient has a decreased range of motion, a therapist will assess the joint before performing an intervention and will continue to use the tool to make sure that progress is made. These range of motion measurements can be taken at any joint and they typically involve some knowledge about the anatomy of the body, particularly bony landmarks. For example, when measuring the knee joint, the axis (point of rotation) would be placed on the lateral epicondyle of the femur, while the stationary arm would be lined up with the greater trochanter of the femur. Finally, the moveable arm of the goniometer would be lined up with the lateral malleolus of the fibula and a measurement will be taken using the degree scale on the circular portion of the tool. The only problem with goniometers is the accuracy of the reading is not always the greatest. Issues with the intra-measure (between measures) and inter-tester (between clinicians) reliability seem to increase as the experience of the examiner decreases. Some studies suggest that these errors can be anywhere between 5 and 10 degrees when completing repeated measures.