sentences:  The sight itself is parallax-free at around 50 yards, meaning that the red dot will not change position "relative to the target" based on eye position at that range.As in other reflex sights, the point of aim will change position based on eye position at other ranges with the maximum error being equal to the diameter of the sight's optical window at short range.There are currently two variants available; the standard CompM4 and the CompM4S, the latter being the same in terms of features and functionality, but having the battery compartment & power control knob mounted near the bottom of the sight instead of near the top.