Abstract: An apparatus and method for the position of a surgical robot, prior to its use for computer-aided surgery, has a probe (37) on the end of a robot, allowing the location of the robot to be registered with respect to a bone (33) to be cut. Prior to the procedure, the location of the robot is also registered with respect to a bone clamp (10) by touching the end of the probe (37) into depressions (15) formed in the clamp surface. If the robot needs to be moved, with respect to the bone, its position can be accurately re-registered by touching the probe tip back into some of the depressions (15) in the clamp. The system allows easy re-registration without the need either for expensive tracking systems or the use of fiducial markers inserted into the patient's bone.