Medical Digital Protractor Goniometer
Poly-fiber blade with inch and metric scales. Digital display with hold function, inside and outside angle measuring, and reversible reading.
 
This device is unique in that you can set relative zero at any point in the rotation of the blades. The most important concept to grasp to master the device is learning to set relative zero at the neutral or starting  point for joint measurement. The neutral or staring point varies depending on the joint. So for example, the starting point (neutral)  for shoulder flexion is the arm at the side, starting point (neutral) for the elbow or knee is the limb in full extension and the starting point (neutral) for ankle dorsiflexion/plantarflexion is the foot at a 90 degree angle to the lower leg. So you must find starting point (neural) for a joint, hit the “Zero” button, rotate the blades and measure a  joint in degrees. To measure the shoulder, close both blades, hit “Zero” and measure. To measure the elbow and knee fully open both blades, hit “Zero” and measure. To measure the ankle close both blades, hit “Zero”, rotate  to 90 degrees, hit “Zero” a second time and measure.