A method determining artillery fire corrections toward a fixed target using a fixed observation system is oriented and equipped with a device measuring orientation of line of sight, a laser rangefinder, a positioning device, and a display screen with fixed crosshair, displaying and moving another crosshair. The method includes: orienting the observation system to display the central crosshair on the target image and calculating target geographical coordinates using distance provided by the rangefinder. If, after firing, the impact and target do not coincide, the method includes, if the orientation is fixed: displaying a second crosshair on the impact image and measuring offset between the two crosshairs, displaying a third crosshair symmetrical to the second crosshair; and orienting the optronic system to position the third crosshair on the target image, the first crosshair coinciding with the impact point image, and actuating the rangefinder to obtain distance between the system and impact.