In both Arma3 and Arma2 operation arrow head the zeroing for telescopic sights has been simple and has required little out of the players.
now I am aware that some optics do have ranging as easy and simple as this but it is not true for all. (the zeroing method would depend on the type of optic)
for example: some optics use the measurement minute of angle (MOA) which is standard for most modern sniper optics and allows immensely accurate zeroing to the exact meter (considering that 1 MOA is equal to 1/60 of a degree (an accurate, small measurement)). not only would this benefit the player in more precise zeroing but it would also be realistic in that it would take time and a small amount of mathematics to align the scope properly. an idea would be to add a table (up to around 2000m) with MOA adjustment amounts for every 100m increment or so (e.g. 100m| 0, 200m| 4, 300m| 12 etc.). (if anyone played ACE for arma2 it was like this).
other optics use milliradian adjustments which are less common but have the same purpose.
this would add a whole lot of realism to the game while at the same time creating a bit of a challenge for snipers and creates a bigger need for spotters causing a sniper team to work more closely and rely on each other more often (giving the spotter something to do other that find the enemy)