Here's how you figure sight correction or value per adjustment increment. The formula is:

Impact error X Sight Radius divided by Range

Make sure and keep your increments in the same terms and I imagine you'd use inches in your case.

As an example, let's say you have an impact error of three inches at 50 yards and your 629 has a 10 1/2 inch sight radius (and you need to measure this dimension carefully).

Therefore: (3 x 10.5)/1800 (50 yards converted to inches) = 0.0175" of sight correction needed to bring your impact point in line with your sights. This amount of correction can be applied to either sights, front or rear, to obtain the point of impact desired.

Hope this helps you.