The rear sight is set on a movable base so that it can be moved to the
right or left and the aiming point shifted accordingly in order to
counteract the effect of the wind on the bullet.
General Rule. To shift the striking point of the bullet to the left
move the rear sight to the left. And, of course, the reverse holds true
when it is moved to the right.
A Specific Rule. One point of windage moves the striking point of the
bullet 4 inches for every 100 yards you are distant from the target.
(One point of windage at 200 yards causes the bullet to strike 8 inches
to the right or left of the line of aim; one point at 300 yards causes a
12-inch deflection of the bullet; one point at 500 yards a 20-inch
deflection, and so on.)