Baseline digital Absolute+Axis Goniometer - 180 Degree LCD scale - 9 inch Arms has integrated Absolute+Axis levels. Powered by 1 x 9v battery, included. The Absolute+Axis (AA) goniometer establishes a "true" vertical or horizontal to the start point of a measurement. Many goniometric measurements require one arm of the goniometer to be positioned either horizontally or vertically. The other arm is then lined-up with the patient's body part. Until now, the practitioner had to "assume" or "eyeball" the vertical or horizontal position. This interpolation is often incorrect and introduces measurement error. The Absolute+Axis goniometer removes measurement variability and allows the practitioner to concentrate on correct placement of the other goniometer arm and the patient's body position. Some measurements the AA goniometer is designed to improve are: shoulder and hip rotation (internal, external); cervical flexion, extension, rotation and side bending; hamstring flexibility; and active ROM.