An adapter can be easily used to assist a surgical navigation system to determine the effector axis or the effector plane of a surgical instrument. The adapter has a body with a geometrical feature, the geometrical feature has a known relation with a navigation tracker device that can be attached to the adapter. When the adapter is held against a surgical instrument in a non-fixed manner, the effector axis or the effector plane of the instrument can be tracked by the surgical navigation system. The method includes a calibration method to determine the known relation between the effector axis or the effector plane and the location of the navigation tracker.