Red., there are several ways to use that optic for rangefinding. The most accurate way is to use the .2 mil stadia lines to bracket the tgt. with. Suppose u have a 10" target that brackets 4.5 of the .2 mil lines. .2 mil is equal to .72 inches at 100 yds. (.2x3.6=0.72) So here's the equation--
10 x 100 / 0.72 / 4.5 = 310 yds.
See how it works. To get even ever so slightly more accurate u should subtract the thickness of 1 line stadia since most people bracket between lines instead of from center of line to center of line.