Army real world 1 degree = 17.8Mil or 6400Mils in 360 degrees
Optical real world 1 degree = 17.4 Mil or 6283 Mils in 360 degrees
Russian is 6000Mils in 360 degrees.
Sweden is 6300Mils in 360 degrees.
1Mil at 1000ft = 1ft
1Mil at 1000yd = 1yd
1Mil at 1000m = 1m
If I remember it correctly.
In WW2 Mil was the common measurement language to describe deflection as a function of lead as viewed at range through a collimating optical gunsight with a 100Mil calibrated reticle. All of our different cannon shoot their round to 1000ft over a different sub 1second time span. During that time your target at any given speed will travel a predictable distance which can be measured in Mils at range. So having a rule of thumb lead holdoff reference point for the expected general speeds you will run into during combat becomes a necessary tool. Other wise you can spend years in this game shooting by trial and error maybe remembering what worked over time.
One of the earliest rule of thumb I remember hearing in this game over a decade ago, lead with the windscreen bars. An interesting real world lead principle that works in this game. A con traveling at 45-90 degrees to your line of travel at a speed, from 100ft to 1000ft at that same speed, your hold off lead will effectively remain the same from the perspective of your gunsight.