A target is outputted to an ideal position in 3D space. A viewer indicates the apparent position of the target, and the indication is sensed. An offset between the ideal and apparent positions is determined, and an adjustment determined from the offset such that the apparent position of the ideal position with the adjustment matches the ideal position without the adjustment. The adjustment is made to the first entity and/or a second entity, such that the entities appear to the viewer in the ideal position. The indication may be monocular with a separate indication for each eye, or binocular with a single viewer indication for both eyes. The indication also may serve as communication, such as a PIN input, so that calibration is transparent to the viewer. The method may be continuous, intermittent, or otherwise ongoing over time.