Zeroing

               Before you do any long range shooting you must make sure that you zero, or sight in your weapon system. This means to match the crosshairs up to where the bullet is impacting a target at a certain range. Most rifles are sighted in at 100 yards. The scopes on these rifles use a "click" system to zero in. The scope has two knobs which turn left and right to move the X-axis of the crosshairs up or down, and the Y-axis let and right. In almost every scope, one "click" moves the crosshairs 1/4 of an inch at 100 yards. The shooter must take an initial shot and D.O.P.E. (Data on previous encounters. in other words, using your previous shots to predict where your next will hit) his scope until the crosshairs and point of impact match up. I used both the link and video below to help illustrate how to sight in a rifle.

http://adventure.howstuffworks.com/outdoor-activities/hunting/traditional-methods/rifle-scope4.htm