Abstract: Orientation can be determined without the aid of a generated source using nine axis Magnetic, Angular Rate and Gravity sensor unit containing three orthogonally mounted angular rate sensors, three orthogonal accelerometers and three orthogonal magnetometers. This study describes a quaternion based complementary filter algorithm for processing the output data from such a sensor. The filter forms the basis for a system designed to determine the posture of an articulated body in real time. In this system orientation relative to an earth fixed reference frame of each limb segments is individually determined through the use of a attached MARG Sensor, The Orientations are used to set the posture of an articulated body model. Details of the fabrication of a prototype MARG Sensors are presented. Experimental results show the effectiveness of the tracking system.