Ballistic drop compensator is special kind of weapon sight crosshair. The game uses ACOG sights which have ballistic drop compensator build in the crosshair. The crosshair used horizontal lines with a single digit number - 4 for 400meters, 6 for 6 hundred meters etc.

The horizontal line is universal ruler for the average male person for that distance. Meaning average male should be as wide as a vertical line with number 4 at distance 400 meters. This way sight can be used to measure distance to person and shoot accurately quickly.

In Arma 3 a person at 400 meters doesnt match the width of horizontal line in sight. This is also true for every horizontal line up to 600 meters. 700 - 1000 meters lines are in accordance with a person width for the given distance.