Vortex Optics RAZOR HD GEN II 4.5-27X56 RIFLESCOPE - Manual (Page 3)

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Reticle Subtensions
MRAD Subtensions
The EBR-1C MRAD reticle is based on the milliradian, or mrad for
short. Mrad unit of arc measurements are based on the radian. A
radian is the angle subtended at the center of a circle by an arc that
is equal in length to the radius of the circle. There are 6.283 radians
in a circle and 1000 milliradians in a radian for a total of 6,283
milliradians (mrads) in a circle. An mrad will subtend 3.6 inches at a
distance of 100 yards (10 cm at a 100 meters). Most riflescopes with
mrad adjustments use .1 mrad clicks which subtend .36 inches at 100
yards (1 cm at a 100 meters).
In the Razor HD Gen II first focal plane riflescopes, the listed mrad
subtensions of the EBR-1C 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.