Vortex Optics VIPER PST 4-16X50 FFP RIFLESCOPE — First Focal Plane - Manual (Page 3)

RIFLESCO PE
5 4
EBR-1 MOA Reticle Subtensions
Heavy crosshair
subtends 5 MOA
Fine crosshair
subtends .21 MOA
Gap subtends
10 MOA 5 MOA 2 MOA
MOA Subtensions
The EBR-1 reticle is based on minute-of-angle (MOA) subtensions.
MOA measurements are based on
degrees and minutes: 360 degrees in
a circle, 60 minutes in a degree for a
total of 21,600 minutes. These angular
measurements are used to estimate
range and correct for bullet trajectory
drop in riflescopes. 1 MOA will
correspond to 1.05 inches at a 100 yard
distance, 2.1 inches at 200 yards, 3.15
inches at 300 yards, and so on.
In the Viper PST first focal plane
riflescopes, the listed MOA subtensions
of the EBR-1 reticle are valid at all
magnification levels. This means the
shooter can use the magnification level
most appropriate for the situation and still have effective holdover and
windage reference marks. This is also extremely valuable in a high-
stress situation, as the shooter does not have to remember to set the
scope to one particular magnification to get valid holdovers—an action
necessary with the more common second focal plane reticles.
Although 1 MOA is very
commonly corresponded to
1 inch at 100 yards, this is
not quite correct. 1 MOA at
100 yards equals 1.05 inches.
Calling 1 MOA an inch per
100 yards may be acceptable
at shorter distances, but it
will cause a five percent error
in ranging and holdover
adjustments. This will result
in missed shots at longer
distances.
Estimating MOA