Abstract: An electronic device for measuring relative angular positional displacement and angular range of motion for body segments and articulating joints of the human skeleton is disclosed. The device has a hand-held interface unit which is placed against the body segment or joint to be tested. Mounted within the housing of the interface unit is a shaft with a pendulum at one end and an optical encoder at the other. As the body segment rotates or the joint articulates, the pendulum swings in the direction of gravity, causing the shaft to rotate. The optical encoder generates an electrical signal representative of the amount of rotation of the shaft. The generated signal is fed to a microprocessor which processes the information and can produce on a display the change in angular position relative to initial angular position or the angular range of motion of the body segment or articulating joint.