Measuring Angles, Not Distances
Aiming adjustments are described in angular units because a fixed angle at the sight grows into a larger displacement the farther away the target sits. The two common units are the minute of angle, abbreviated MOA, and the milliradian, abbreviated MRAD or mil. Both measure the same kind of angle; they simply divide it on different scales.
Minute of Angle
One MOA is one-sixtieth of one degree, since a full circle contains 360 degrees and each degree is split into 60 minutes. At 100 yards this angle subtends 1.047 inches, which shooters usually round to a convenient one inch. That neat correspondence with yards and inches is why MOA is popular in imperial-unit contexts.
Milliradian
A radian is the angle whose arc length equals the circle's radius, and a milliradian is one-thousandth of a radian. Because it is defined by the radius directly, one mil subtends one unit of distance at one thousand of the same units: 10 cm at 100 m, or 1 m at 1000 m. This clean scaling makes the mil natural for metric ranging and adjustment.
Clicks and Turret Values
Optics adjust in discrete steps called clicks, and each click moves the point of impact by a fixed angular amount. Common values are 1/4 MOA per click or 0.1 mil per click. Reading the turret marking tells you how far each click shifts impact, which is essential for translating a correction into the right number of clicks.
Matching Reticle and Turrets
An optic is easiest to use when its reticle subtensions and its turret clicks share the same unit. If the reticle measures a miss in mils, mil turrets let you dial the exact value seen. Mixing an MOA reticle with mil turrets forces a conversion on every shot and invites arithmetic errors.
Worked Example
Suppose at 100 yards your impact is 2 inches low. Since 1 MOA is about 1 inch at that distance, you need roughly 2 MOA of upward correction. On a scope with 1/4 MOA clicks, that is 2 divided by 0.25, or 8 clicks up. On a 0.1 mil scope, 2 inches is about 0.56 mil, which rounds to 6 clicks of 0.1 mil each.
A Common Misconception
People often treat 1 MOA as exactly 1 inch at 100 yards and 1 mil as exactly 3.6 inches, then assume the small rounding never matters. The true value is 1.047 inches per MOA, so at 1000 yards that rounding grows to nearly half an inch. For close work the approximation is fine, but at long distance the exact figure should be used.