Yards:
The 1901 Krag sights are unique in they have a variety of sighting options.
Look at the picture you posted. First take the slider. When the sight is laid down as pictured. Using the rear notch you set the rifle on Battle Sight. On the left side of the sight is the letter "B" and yard markings. The rifle is carried in normal conditions with the slider set so the notch is lined up on the B, (BSZ) which would is set for 375 yards. You can use this sight for 100 to 400 yards.
The other mark on the slider is used when the sight is flipped up. It goes from 450 to 1900 yards.
The peep in the rear of the slider (when the sight is flipped up can be used from 100 to 1775 yards.
The at the top of the sight when its flipped up is set at 2000 yards.
At the front of the sight is a lever that you loosen so you can pivot the rear sight for windage changes. The windage marks on the rear sight are 0.04 inches a part. each movement per mark moves the impact 5.56 in at 100, 11.74 at 200, 17.69 at 300 and 58.8 at 1000 yards, (rather course).
The sights settings are based on a 220 gr RN bullet with a MV of 2000 fps.
I use that load in my Krag with the 1901 sights and found the sight markings are pretty accurate. I find the peeps a little slow to find the front sight so for fast shooting I use the notch on the slider. I don't shoot this rifle much past 400 yards any way, but I have done it, its just not that fast.
I used my '98 Krag w/1901 sights in a three gun match and it worked quite well, except it's slower to re-charge the mag then the ARs most people were using. One stage had some really close balloon targets and since I was limited to six rounds they let me use the bayonet on the balloons to save one reload. When the sight is laid down you can side it back a bit short of the 100 yard mark that allows you to shoot 25-50 yards. (Bayonet changed impact but not too bad at close range).
It was quite an experience.