The invention relates generally to a user interaction system having a head unit for a user to wear and a totem that the user holds in their hand and determines the location of a virtual object that is seen by the user. A fusion routine generates a fused location of the totem in a world frame based on a combination of an EM wave and a totem IMU data. The fused pose may drift over time due to the sensor's model mismatch. An unfused pose determination modeler routinely establishes an unfused pose of the totem relative to the world frame. A drift is declared when a difference between the fused pose and the unfused pose is more than a predetermined maximum distance.