Many goniometric measurements require the practitioner to place one arm of the goniometer in either the horizontal or vertical position. The other arm is then lined-up with the patient's body segment. Until now, the practitioner had to "assume" or "eyeball". The integral absolute vertical and horizontal levels are permanently incorporated in the digital goiniometer arm. Goniometer reads 0-180 degrees on LCD screen. Has ability to freeze angle measurements. Powered by 1 9V battery. Exterior is powder-coated steel with inch/cm marks screened onto arms. For more information, please take a look at the downloadable manual (above the big sign-up image on the right side).