The Goniometer (GNM-BTA) comes with a set of flexible arms that vary in size. For subjects with smaller limbs, you may want to use one of the smaller joint arms on this sensor. To change the flexible arm, simply loosen and remove the screw that secures the arm to the dial. Select the appropriate joint arm and fasten it to the sensor with the screw provided. Verify that the terminal edge of the joint arm is aligned with the set screw on the side of dial. Reposition the flexible arm of the Goniometer if necessary. Follow the directions for calibrating the sensor that can be found in the sensor booklet.