Patent US 4,777,352

A microcontroller operated optical device for determining the distance to objects of known or estimable size which is programmed to control a movable indicator relative to a stationary indicator for spanning a dimension of an image of an object. The distance spanned by the movable indicator is inversely proportional to the distance of the object from the apparatus and the microcontroller subsequently interprets the span in terms of the distance to the object and displays the resultant distance for viewing by an operator. This device is usable in surveying instruments, riflescopes, telescopes, binoculars, and the like, and is controllable by an operator who selectively activates it by, and with, known data. In riflescope embodiments the microcontroller is further programmed with ballistic data and, subsequent to rangefinding, calculates a holdover factor to compensate for deviations in the flight path of the bullet to be fired by the firearm to which the device is attached from the line of sight through the apparatus and selectively activates the movable indicator to move it to a second position to provide an accurate aiming reference compensatory of the deviations in the flight path.