With the sight folded DOWN, you can only use the top aperture. This is a general-purposes battle sight.
For accurate shooting, you use the LOWER of the two apertures when the sight is standing up. This is the aperture in the thin little cross-slide; you adjust it for Left-and-Right with the wormwheel BEHIND the thin leaf.
For RANGE, you have TWO scales, one in HUNDREDS OF YARDS (a Yard being 36 inches or 3 feet or .9144018 of a METRE), the other scale in MINUTES OF ANGLE. You use this one with uncertain ammunition or, if on a range in a match or shooting under direction, by whatever figure is given to you by the Team Captain or the Commanding Officer. The scale in Yards is, of course, designed for the performance of Mark VII Ball ammunition: a 174-grain 3-piece composite impact-unstable bullet at a nominal muzzle velocity of 2440 ft/sec as measured with the SMLE rifle. This will be about 125 to 150 ft/sec FASTER coming out of a Ross: that extra 5 inches of barrel does make a difference. If your barrel is cut to the normally-seen 25 or 26 inches, then you have less worries.
Hope this helps.
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