This transparent plastic goniometer permits observation of a joint's axis of motion and its range of motion. The unique design adds a white line behind the measurement gradations to make the readings even easier to read. The primary purpose of this device is to assist in physical therapy by determining range of motion of a joint as well as evaluating and gauging recovery after surgery or physical therapy. The 360° head has three scales calibrated to be used with the ISOM (International Standards of Measurement, STFR) system. This is an essential tool for treatment, rehab and surgical recovery and evaluation. Given its convenient shape and size, this is suitable for home use as well as multi-user environments. The arms are 6". This is a pack of 25 units. This goniometer lets you measure joint limits and range-of-motion as well as check extension, flexion, abduction, adduction and rotation. The arms have a linear scale in both inches and centimeters. They also will remain at the last measurement position until reset. The 360° angle scale reads 1° increments. The clear plastic of the goniometer allows the device to be placed directly and exactly on a joint or limb for easy observation. This Goniometer is a Baseline product, which means it's a trusted name in measurement and evaluation instruments. Baseline products have been used by Medical Professionals, Therapists, Doctors and Rehab Clinics all over the world since 1974. If you have ever received therapy after an injury, you have probably had your progress tested and measured with a Baseline measurement instrument.