Hello there! I thought I'd detail the use of mil-dot sights for ranging, for the unfortunate sniper-spotter pair who find themselves without rangefinders.
I'll eventually update this thread with using the sights to figure out gun elevation, if for some reason you don't want to adjust the range (or don't have time to).
I've made a video, which you can watch below, or just read the explanation that follows it (with pictures!).
So this here is a mil-dot reticle that is found in many of the sniper scopes in Arma 3:
(Does re-sizing not work?)
The distance between two dots is 1 mil (the centre dot is removed for aiming purposes, but still counts as a dot). 1 mil is an interesting quantity, it translates 10cm when the target you're looking at is 100m away, and scales proportionally to 1m when the target is 1km away. I can't really relate to a yard so I'm going to stick to the S.I./metric system.
Anyway, this property can be used to figure out how large something is if the distance to it is known, or how far left or right to aim, or how far something is if the size of that object is known. How? Like this:
Now a man in Arma 3 is probably 6 ft tall, or 72 inches, or 1.82m. You can approximate this to 1.8 or 2 depending on what you'll have to divide it with; so 2/4 mills is easier than 1.8/4 (unless you're much better at math than I am) but 1.8/6 is easy (and more accurate?) than 2/6.
Of course, if you or your spotter carries a field calculator, then go ahead and use 1.82.
This picture is pretty self explanatory. Probably using 1.82/2.8 would be more accurate (0.65 x 1000 = 650m, which is much closer to the actual distance) but for the purpose of telling your squad mates or changing the range on your rifle, 600 is a good enough estimate (I suppose?).
You could always verify using the map, of course. Each side of the grid squares being 100m, Pythagoras will tell you that the diagonal is about 140m.
I was lying down in the grass a bit beyond what's shown in the map when I took that screenshot, and the target wasn't the same (but very close), so he was probably about 650m away.
That's about it. Watch the video for a 3 target demo at various ranges, I've also used a range finder to verify my estimates.
I'll update this post when I finish editing the other video about guessing elevation (unless of course someone has a ready source for that, in which case please do save my efforts
).p.s. I hope this meets Party standards!
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Further reading:
http://www.mil-dot.com/articles/the-mildot-reticle
http://www.millettsights.com/resources/ ... holdovers/
http://www.mil-dot.com/media/1027/the_d ... ations.pdf
