Good question Len. This is where reverse "milling" helps to understand the error that can be expected from the system. OK, suppose u're using the TMR reticle that has super-fine ranging stadia at .2 mil (.72 IPHY). You're hunting antelope in WY, and u've snuck up to the edge of a shallow basin, and there the big 1 stands way out there (assume 15" back to brisket for a buck according to the Kahles website). Now at 500 yds. he would bracket 4.2 subtension units--
15 x 100 / .72 / X = 500
X= 4.2
Now suppose u're +/- .1 subtension units off with that reticle. Here's the range of error--
4.1 = 508 yds.
4.3 = 484 yds.
miss or hit?? Depends on the cartridge assuming a 10" vital zone (pg. 105 of Bob Hagel's "...Game Loads and Practical ballistic for the Amer. Hunter--great book, BTW, IMO). Of course u're aiming dead center on his chest, so that means +/- 5".
OK, now he's +/- 1" chest depth measurement @ 4.2 subtension units--
14 x 100 / .72 / 4.2 = 463 yds.
16 x 100 / .72 / 4.2 = 530 yds.
...so???
700 YDS. =
15 x 100 / .72 / X = 700
X = 3.0 SU's
15 x 100 / .72 / 2.9 = 718
15 x 100 / .72 / 3.1 = 672
14 x 100 / .72 / 3.0 = 648
16 x 100 / .72 / 3.0 =741
...so???
It's my opinion that any subtension unit has an interpolative accuracy of .1 of it's total subtension--
TMR = .1 x .72 IPHY = .072 IPHY accuracy
MD = .1 x 3.6 IPHY = .36 IPHY accuracy
This is why i like the finer stadia, as it does help somewhat.
Now, how important that is for big game depends on the individual to make that decision--for a coyote or chuck tho., at least for me i don't really care. I'll hurl 1 his way.