What's with Battlefield 4's range toggling on sniper rifles?

I was playing through the campaign and when I first wielded a sniper rifle a tutorial popup appears at the top-right corner of the screen, explaining something about bullet drop distance and the alternate fire key (the key to toggle single fire/burst fire/auto fire on automatic rifles).

I was in the heat of a gun fight so I didn't have the time to read through the popup, but then I noticed if I press the alternate fire key with a sniper rifle, there is a distance indicator at the bottom of the screen in place of the fire mode, and I can toggle it between 0m, 100m, 150m (I don't remember the exact number).

I'm wondering if anyone read through that tutorial bubble and can tell me what that means, I searched online but there's no information regarding this, and I don't wanna play through my campaign again just to read that bubble...

Solution 1:

It is the zeroing mechanism. This means that if you have it zeroed at 500m, the cross-hairs are dead on at 500m. This allows you to make distance shots much easier. If you were to zero the scope at 500m and shoot at a target at 100m, your shot would hit much higher than your cross-hairs. Previously, your only option was to compensate for bullet drop by aiming high and guessing between mil dots, which made distance shots on moving targets much more difficult. If you have your scope properly zeroed, now you can just offset the horizontal reticule the appropriate lead for motion.