A battery-powered device used to measure the functioning of normal or abnormal joints (e.g., a knee) in order to evaluate the slackness and/or displacement in the motion of the joint (i.e., the joint laxity), usually by measuring ranges of motion, acceleration, or forces exerted upon the joint. It may be employed in the assessment of other characteristics of the joint, e.g., stability and/or anterior/posterior tibial displacement. This device is typically used for reconstructive surgery to evaluate and control joint laxity and stability of the knee and the length of the reconstructed ligaments.