Abstract: The arrangement is of the type comprising: an optical sight (200) combined with an afocal opto-electronic unit (300).According to the invention the opto-electronic unit is located in front of the entry window (210) of the optical sight and the light rays emitted by a reticle (250) are guided from the optical sight (ABC) thus passing through its entry window (210), then towards the exit window (320) of the opto-electronic unit (CDEFG) in order to make the rays emitted by the reticle follow the same optical path (GHIJ) as the rays emitted by the object to be observed (400).The angular deviations produced by the addition of the opto-electronic unit are thus compensated for.In order to measure the magnification produced by this addition, the reticle (251,251') is split by a known value (1) the distance (1') between the images of this split reticle is then measured by a row of diodes (280), (FIG. 2).