Oh, man! Please, a little more respect here! Remember that this forum is for members to ask questions and get help from other members. It is not a vehicle for members to slag off on each other.
I always find that the whole subject of mils and moa is very poorly understood by the shooting community. Even the many "expert" videos on the subject do more to confuse than enlighten.
First, understand that a mil, or milliradian, is by definition a thousandth part of a radian. And a radian is an arc (or part of a circle) whose length is equal to the radius. So at a range (or radius) of 100 yards (3600 inches), 1 mil = 3.6 inches EXACTLY. And at 100 meters, 1 mil = 10 cm EXACTLY. To revert to the original example, there are 43,200 inches in 1200 yards, so at that distance 1 mil = 43.2 inches EXACTLY. And a correction of 425 inches is therefore 425 / 43.2 = 9.838 mils. Note that the value derived by TANGENT using the arctan trig function is ever so slightly different from this because we're dealing with spherical measurements here rather than perfect triangles. But at this level of precision we are stepping out of the real world and into the world of mathematical fantasy, for shooting purposes. So let 9.8 mils stand.
Just keep this 1:1000 relationship in mind and forget all the other formulas you've ever heard on the subject of mils.
Second, understand that the common use of 1 moa = 1 inch at 100 yards is an APPROXIMATION for convenience in the field. For practical purposes the approximation is useful and sufficiently accurate. A more precise value is 1.0476 inch, but let's not get anal here. For precise calculations, you need to be aware that the error of 0.05 inch per 100 yards may accumulate to something significant when you're shooting past your back fence. (My back fence is a long way out.)
Again, please mind your manners, folks. Trolls aren't welcome, and no one likes a wise guy.
