In other studies, systems with accelerometers, gyroscopes, and magnetometers were used to measure the orientation of different body segments [20]–[24]. Accelerometer and gyroscopes were used to estimate inclination and orientation. Magnetometers were used to measure orientation around the vertical axis, assuming uniform local magnetic field. Bachmann et al. investigated the effect of magnetic disturbance on the accuracy of orientation tracking systems and observed errors that ranged from 12◦ to 16◦ [25]. Yun et al. presented a simplified algorithm for orientation estimation using only accelerometers and magnetic field measurements [26]. The gyroscope-free system was only suitable for tracking slow movements. Cutti et al. used inertial and magnetic data to measure arm kinematics in one subject performing tasks involving shoulder and elbow single-joint-angle movements [27] and obtained an average RMSE ≤ 3.6◦.