Bill,
Many Leupold scopes have this Range Estimator feature. This is from Leupolds website:
Range Estimating
Selected Vari-X III scopes have a built-in range estimator. Its a simple system that uses the Duplex® reticle and two sets of numbers on the power selector ring. The numbers facing front show the scopes magnifications. The numbers facing back show distances in yards and meters.
Looking through the scope, the space between the tip of the thicker post and the center of the reticle covers 16" at 200 yards, when set at low power.
So lets say youre targeting a deer whose body is 16" backbone to brisket. Adjust the power selector so that the deers body fits between the center of the crosshair and the top of the lower heavy post. Then, read the approximate distance in yards, from a minimum of 200 at low power to a maximum of 600 at high power.
Hopefully this helps out, if not let me know.