Disclosed are a system, apparatus, and method for calibrating an optical see-through display (OSD). The OSD virtual display size is estimated as a starting point for determining an eye to camera distance. In response to determining the eye to camera distance and comparing the result with a measured eye to camera distance an updated display size may be determined. A user's head movement may be tracked in order to determine when a visual alignment based calibration routine is complete. When a user is not viewing a calibration target a request is sent to prompt the user to realign the OSD. When a user is still after a period of alignment with the OSD, the alignment and calibration procedure may be assumed as complete. A buffer may receive calibration values from before and after the calibration procedure is complete and the values may be averaged or filtered for accuracy.