A device for determining relative orientation between two locations including an imager, an inertial-orientation-sensor firmly attached to the imager for determining information relating to the orientation thereof and which exhibits drift and a processor coupled with the imager and with the inertial-orientation-sensor. The processor determines a first orientation-measurement and first time-tag when the device is oriented with a first-orientation-indicator located at a first location. The processor determines a second-orientation-measurement and second time-tag when the device is oriented with a second-orientation-indicator located at a second location. The processor determines a third-orientation-measurement and third time-tag when the device is oriented again with the first-orientation-indicator. The processor determines the drift associated the inertial-orientation-sensor according to difference between the first-orientation-measurement and the third-orientation-measurement the respective time-tags associated therewith. The processor determines an angle-difference between the first-orientation-indicator and the second-orientation-indicator according to the first-orientation-measurement and the second-orientation-measurement, the first and second time-tags and the drift.