Two shot zero:
Put your rifle on sandbags, aimed at a small target in the middle of a larger sheet of paper.
Center the crosshairs on the target.
Fire one shot.
Now, center the crosshairs back on the target, and make sure the rifle is solidly in the sandbags.
Take your dime, or whatever, and fiddle with the screws until the crosshairs point at the bullet hole.
Fire one shot at the target to be sure.