Leupold RX Operating Instructions Manual page 23

For best results, measure the drop of your arrow at 40 yards from your 20 yard
aiming point.
1. Set up a small target point such as a two-inch circle of paper high on a
large, safe background, such as a stack of bales backed by a solid backstop.
Be sure to allow for three feet or more of drop to avoid arrow damage.
2. Shoot 2 or 3 arrows at the target from 40 yards, using your 20 yard pin
on the small target.
3. Measure the distance from the small target to the center of the group
of arrows.
4. Select your TBR bow group from the "Drop from 20 yard pin at 40 yards"
column above.
Only use initial velocity for determining your bow group if you have obtained a
chronograph measurement of your arrow speed. Bow manufacturer's published
speeds such as IBO speed are based on standard draw lengths and weights
that are not likely to be the same as with your bow, therefore the actual
performance will not be the same.
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