The first thing to commit to memory is FORS. This stands for Front Opposite, Rear Same. When you want to move the point of bullet impact on the target, you move the front sight in the OPPOSITE direction or you move the rear sight in the SAME direction.
For example, if the gun shoots low
you need to raise the bullet's point of impact. To accomplish this you
need to raise the rear sight UP,
the same as the desired point of impact.
FORS holds true for windage adjustments as well. If your pistol is shooting to the right, you want to change the point-of-impact (POI) to the left. To accomplish this you have tow choices. You can either move the rear sight to the LEFT (Rear Same) or move the front sight to the Right (Front Opposite). For most non-adjustable sights you can make these changes by drifting the appropriate sight in it's dovetail. To do this, lay the pistol on a piece of carpet or several doubled shop rags and gently tap the slide with a brass drift. More often than not, you'll find that you have to abandon “gently” and give it a “real” adjustment (i.e. a bigger hammer and more muscle.)
You can calculate the amount you need to move the sights by grabbing your calculator and doing the following:
Multiply the sight radius (in inches) by the number of inches of impact movement, divided by distance to the target in inches.
Example #1: A rifle with an 18-inch sight radius is shooting 6 inches high at 100 yards yields (18 x 6)/(100 yards x (36 inches/yard)) = 0.030-inchs. This will require you to RAISE the front sight 0.030 inches to achieve the desired adjustment at 100 yards. Conversely, you could LOWER the rear sight by the same amount to accomplish the 6 inch movement.
Example #2: Colt 1911 with a 7-inch sight radius shooting 2 inches low at 10 yards yields (7 x 2)/(10 yards x (36 inches/yard)) = 0.0389 inches. So you need to raise the rear sight or lower the front sight by this amount.
Example #3: Colt Commander with a 5.5-inch sight radius shooting 3 inches high at 7 yards yields (5.5 x 3)/(7 yards x 36) = 0.0655 inches of sight adjustment. You will need to lower the rear sight or raise the front sight by this amount.