Mildot Windows

On a mildot reticle there is a square area covered by the thin crosshairs which is 10 mils across. Let's call this the "Big Window". The Big Window is divided into 4 "Small windows". The Big Window is one yard across at 100 yards, Small window 18" at 100 yards. The Big Window is one foot across at 100 feet, Small window 6" at 100 yards. The Big Window is one meter across at 100 meters, Small window 500mm at 100 m. If this is all you can remember, you can do rangefinding if something on the target is a foot across, a yard across, 6" across and so on. Plus on "2nd focal plane" mildot scopes, the area covered by the Big Window is changed by the Zoom knob. So you can turn the Zoom knob down to get a 50" Big window at 100 yards (make a note of this zoom setting), with each mildot covering 5" @ 100 yards. Or a 40" Big window. Or whatever suits you. So you have a rangefinder you can actually remember how to use. Note: First focal plane reticles zoom in sync with the target, so the Big Window always covers the same area at a given range.

Mildot windows for ranging

OK, let's say the target has a reference of 36" on it somewhere. Height of the target stand, shoulder height of animal or whatever. 36", or one yard is 10 mils at 100 yards, so it covers the "Big Window" exactly. At 200 yards 36" is half the "Big Window", 400 yards a quarter of the Big Window and so on. If you have a known distance of 36" on the target, this is super easy to remember. For an 18" target, use the small window. At 200 yards 18" is half the "Small Window", 400 yards a quarter of the Small Window and so on. So if you have 18" or 36" on the target, you can do rangefinding in a few seconds without computers, paperwork or hard math. If the target is 12" across, it fills the Big window at 100 feet, At 200 feet 12" is half the "Small Window" and so on. A 6" target fills the Small window at 100 feet, you get the idea.