When aiming with a rifle scope, two different points need to be lined up: the sighting point and the aiming point on the target. The reticle must not be displaced by external forces such as recoil, otherwise the impact point will vary uncontrollably. However, in order to sight in the firearm, it must be possible to move and adjust the reticle inside the rifle scope.
The aiming point is the point on the target object at which you are aiming. When using open sights, both back and front sights must be lined up with the aiming point for an accurate shot. With a rifle scope, the back and front sights are, as it were, brought together into a single point on the reticle, the sighting point.
The click settings are used to adjust the reticle in the turrets on the rifle scope. The relevant direction is indicated by the label on the turrets. Each click changes the impact point at 100 m (109 yds), e.g. by 1 cm (0.39 in).
The displacements of the reticle this produces in the reversal system are in the thousandths of a millimeter.