Vortex Optics VIPER PST 1-4X24 RIFLESCOPE - Manual (Page 3)

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RIFLESCOPE
Depending on which version you have purchased, your Viper PST
1–4x24 riflescope will feature adjustments and reticles scaled in MOAs
or mrads. If you are unsure of which scale is used, reference the top of
the adjustment turret.
If the adjustment is in MOAs,
the turret will display
“1 Click = 1/2 MOA”. If the adjustment is in mrads,
the turret will display
“1 click = .2 mrad”.
The Subtension Scale: MOA or MRAD
Both minute-of-angle (MOA) and milliradian (mrad) unit of arc scales
are effective when ranging or adjusting riflescope for bullet trajectory.
MRAD Adjustments
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 all circles and
1000 milliradian in a radian for a total of 6283 milliradians (mrads) in a
circle. An mrad will subtend 3.6 inches at a distance of 100 yards. Viper
PST 1–4x24 riflescopes with mrad adjustments use .2 mrad clicks which
subtend .72 inches at 100 yards, .1.44 inches at 200 yards (4 cm at 200
meters), 2.16 inches at 300 yards (6 cm at 300 meters), etc.
MOA unit of arc measurements are based on degrees and minutes.
There are 360 degrees in a circle and 60 minutes in a degree for a total
of 21,600 minutes (MOA) in a circle. A minute of angle will subtend
1.05 inches at a distance of 100 yards. Viper PST 1–4x24 riflescopes
with MOA adjustments use 1/2-minute clicks which subtend .52 inches
at 100 yards, 1.05 inches at 200 yards, 1.57 inches at 300 yards, etc.
MOA Adjustments
Second Focal Plane Reticle
This PST riflescope model uses a second focal plane (SFP) reticle.
The advantage of a SFP reticle is that it always maintains the same
appearance. Shooters using reticle hashmarks should be aware that
the listed subtensions used for estimating range, holdover, and wind
drift correction are only accurate at the 4x magnification.