Re: Metric mil reticle subtension...coincidence?
As folks have already said, there was an expression you learned in high school that went like:
Arclength = Radius * Angle
In fact, since the concepts of arclength and radius are more simple, that is actually the formal definition of what an "angle" is. This is just a generalization of the expression
Circumference = Radius * (2 * pi)
so now we know the angle 2pi is equivalent to "all the way around the circle" and we call this unit of measure for angles "radians", i.e., a circle is 2pi radians. In this sense, the radian is the natural unit for describing angle.
Knowing this, it should be obvious that if both the angle (in radians) and the radius are strictly powers of 10, so should the arclength. It doesn't matter if you're measuring distance in meters, yards, feet, inches, whatever: as long as your adjustment is not too far from level, for any abitrary length unit, (x radians) at (y length unit) distance = (x*y length unit). This may be be why some prefer mils to MOA.
(There is some subtlety because when you talk about making a 1 mil adjustment on a flat sheet of paper 100 meters away, it's not exactly arclength but instead the arclength projected onto the plane of the paper, but for 1 mil, that difference is tiny).
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sscoyote</div><div class="ubbcode-body">So if the 1/6400th part of the circle is used then the "milli"- prefix is technically incorrect</div></div>
No, it's still correct.
You're confused because the total number of radians in a circle is not unity or a power of 10. It's 2pi. I.e., 1 radian is not a full circle, 2pi radians is.
A milliradian is 1/1000 of a radian by definition. There are 2pi radians in a full circle, meaning there are 2000pi milliradians in a circle, so that each milliradian is 1/2000pi ~ 1/6283 of a circle.
But that really has no bearing. Just remember the arclength expression.