Vortex Optics VIPER PST 6-24X50 RIFLESCOPE - Manual (Page 4)

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RIFLESCO PE
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.
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 1/4s if possible.
Ranging
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.
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 (72 inches) at 10 MOAs yields 688 yards.
72 x 95.5
10 MOA
688 Yards =
Target Size (Inches) x 95.5
Measured MOAs
Range (Yards) =
MOA Ranging Formula
Example