[Baldo_the_Don]

I've been attempting this reply for a few days. I might manage it now. It might be long.

TL;DR: I think good modding needs decent math, and decent math works in mods of every game. Lessons may overlap.

Basic info:

The screen shot of the soldier clipping through the crate is to illustrate that the 101st Airborne logo on the crate is almost a dude wide.

The photo of the page from an old german military training manual shows how the german reticle #1 can be used to estimate range.

Then the screenshot of the crate through the scope of the Kar-98 from the bunker. The careful observer may notice how everything but the front of the crate is invisible. Day of Defeat has a fog mechanic editable through the console and .cfg files. I set the fog to start at 2626 map units away, and end 2627 map units away. Tells you little 'til I explain that each map unit is .75 inches, so 2626 x .75 = 1969.5 inches x 2.54cm/inch = 5002.53cm, or a bit over 50m. Also note that the almost dude-wide Airborne logo is almost as wide as the gap in the horizon of the reticle, as the old german training manual would lead you to expect.

I did that on purpose.

Now I call your attention the dod_reticle_sprite. The sniper scope reticle sprites in Day of Defeat are 256 px square, contain 4 frames, each frame being one quadrant of the reticle. The tricky bit is knowing about the highlighted areas in that image. Each 256 px² quadrant is mounted in-game excluding the outer 25 px and the inner 2 px, or more clearly, only 229 px² of each quadrant is visible in-game, meaning the reticle graphic is actually 458 px wide.

I calculated the gap in the horizon of the Kar-98 reticle like this: what I call 'dude-wide' is 19", or 48.26cm, a standard target width. A circle with a 50m radius is 50 x 6.2831853 = 314.16927m in circumference (I've memorized rad, 6.2831853, specifically for this kind of math). 0.4826m ÷ 314.15927m = 0.0015361, which is the proportion of a circle with a 50m radius that target covers, and if we multiply that by 6400 mils, we establish that the gap should be 9.83104 mils wide (or 9.6516009 mrads, or 0.552996°, or 33.17976 moa, as you prefer).

I'm not including notes and screenshots of this, but I confirmed to the best of my abilities that the zoom field of view on all sniper scopes in Day of Defeat is 22°. 22° is 391.11111 mils.

A 9.83104 mil gap divided by a 391.11111 mil fov gives us a proportion of 0.0251361, times a 458px reticle graphic is an 11.512333px gap.

Round that up to 12 px. See in the sprite graphic that from the in-game visible center to the edge of the gap is 6 px on each side. See the through-scope screenshot how close I got it.

You might see that the absolutely anachronistic illuminated rangefinder reticle has dude-wide subtensions at 50m. That reticle is not only not WW2 era authentic, it's also very wrong for the magnification, but it was fun to do. It is internally correct, though. The crosshair subtensions are 1 moa each, so the 100 yard line at the top of the choke is a little more than 17 moa at the inside edge of the curves. That equates to 18" wide at 100 yds. Each line (2 moa) below the other is 18" wide 25 yds further away, as far as my math is not wrong. Speaking of which, my one calculation says this reticle requires a 70x magnification, the other says 65x. A third says 25x. Iunno...

I think if I knew how to do sin, cosin, and tangents, I'd get stronger results, but that's beyond me. Sometimes, close-enough-for-government-work is the best I can do.

Also, scope sway on the sniper rifles in this game is non-stop and random, it's less when you go prone, but never gone. No breath control key. All you can do is work against it and hope. A lot of screenshots were also ruined by the artillery shaking things up so often.

The Half-Life mod I tested the scope zoom in had an FOV limit of 10°, I'm assuming all HL mods have the same limit. And lastly, very few of the maps in Day of Defeat had any sightlines 50m or longer. I highly doubt you'll find a 100m sightline anywhere in this mod at all.