In physical therapy, occupational therapy, and athletic training, a goniometer measures range of motion of limbs and joints of the body. These measurements help accurately track progress in a rehabilitation program. When a patient has decreased range of motion, a therapist assesses the joint before performing an intervention, and continues to use the tool to monitor progress. The therapist can take these range of motion measurements at any joint. They typically require knowledge about the anatomy of the body, particularly bony landmarks. For example, when measuring the knee joint, the therapist places the axis (point of rotation) on the lateral epicondyle of the femur, and lines up the stationary arm with the greater trochanter of the femur. Finally, the therapist lines up the moveable arm of the goniometer with the lateral malleolus of the fibula, and records a measurement using the degree scale on the circular portion of the tool. Reading accuracy is sometimes a problem with goniometers. Issues with the intra-measure (between measures) and inter-tester (between clinicians) reliability may increase as the experience of the examiner decreases. Some studies suggest that these errors can be anywhere between 5 and 10 degrees.