Vortex Optics VIPER HS LR 6-24X50 RIFLESCOPE — First Focal Plane - Manual (Page 4)

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Using either the vertical or horizontal MOA scale, place the reticle on
a target of known dimensions and read the number of MOAs spanned.
You will obtain maximum accuracy in ranging by calculating exact MOA
measurements. MOAs should be estimated in 1/2s if possible. To help
calculate this, the XLR reticle uses 1 MOA graduations on inner portion
of horizontal crosshair and 1/2 MOA graduations on outer part as well
as upper part of vertical crosshair. Windage dots are marked in 1 MOA
increments.
Accurate measuring will depend on a very steady hold. The rifle should be
solidly braced using a rest, bipod or sling when measuring. Once you have
an accurate MOA reading, use the formula to calculate the distance.
Ranging
MOA measurements are very effective for ranging using a simple
formula. To use this formula, the shooter needs to know the size of the
target, or nearby object, in inches.
MOA Ranging Formula
Note: In the MOA ranging formula, a shooter may substitute 100 for 95.5
in the interest of speedier calculations. Be aware that this will produce a
five percent over-estimation error of the yardage distance obtained.
Ranging a 6-foot target stand (72 inches) at 12 MOAs yields 573 yards.
72 x 95.5
12 MOA
573 Yards =
Target Size (Inches) x 95.5
Measured MOAs
Range (Yards) =
Example