One shooting related term that is almost always misinterpreted by newbies, and non-newbies alike is the minute of angle measurement. As a rule of thumb a minute of angle is accepted as close enough to an inch at 100yds. Which is close enough, generally.
MoA is not a lineal but an angle measurement, and I consider it a dispersion angle. The measurement of this dispersion on a target at range is what we consider the 'MoA' thing. Note that angle is measured either in decimal x.xx or in fractions being degree, minutes and seconds, so degree of angle, minute of angle and second of angle. Use of the 'of angle' is to prevent confusion, as degree is used for other things, temperature, angle others too. Without getting into radians... a degree is 1/360th of a circle or a full rotation from an origin. A minute is one 60th of a degree and a second is one 60th of a minute.
As far as math goes.... Minute of angle is basic trig, a minute is one sixtieth of a degree(1MoA) measured from the point is discharge, the muzzle, calculated as follows;
{tan rule, opposite on adjacent}
tan(1/60) = dispersion measurement (distance between bullet impacts) [ divide by ] distance.
Resolve for dispersion height(dh) :
tan(1/60) [ multiply by ] distance = dispersion measurement (distance between bullet impacts)
Once you have a unit 'MoA' measurement you can factor it to any distance, so if you insert a range of 1m (as opposed to 100m) you multiply the result for any range in metres. You can also start with yards if you're that way inclined;
Therefore
(Metric)
tan(1/60) [ multiply by ] 1000mm (1.0m distance) = 0.291mm
100m = 29.1mm
1000m = 291mm
(Imperial)
tan(1/60) [ multiply by ] 36 inches (1.0 yd distance) = 0.01047 inch
100yd = 1.05 inch
1000yd = 10.47 inch
