Abstract: This patent defines a device for automatic calibration of optical sights for firearms. Only one shot has to be fired to achieve this. The device can be integrated with an optical sight or fitted as a separate unit mounted on the sight. The device consists of a digital camera (e.g. CCD), a beam splitter, a microprocessor including a memory for camera images and computer software, servo motors including a gear mechanism, an electrical switch and light emitting diodes and a shot detecting sensor. In the digital sight application, the device also includes a display unit while servo motors, gear mechanism, light emitting diodes and beam splitter are excluded. The calibration procedure involves firing a round at a target consisting of a rectangular white surface on a dark background at the chosen range. The camera saves the last image immediately before the firing moment and compares the cross-hairs position with that of a following image from which the projectile point of impact can be found.