HK offers fixed diopter sights for their HK416/MR556 rifles. The rear sight drum has different sized openings set at different heights for 1, 2, 3, and 4 hundred meters.
There are two versions of the rear sight for different barrel lengths. They are marked by dots under the 200m aperture. The model for the 10.4 inch barrel has 1 dot, and the model for the 14.5 and 16.5 inch barrels have 2 dots under the 2.
The single dot shows that this model is for the 10.4 inch barrel.
The front sight isn’t adjustable, so the rear sight has to be adjusted for elevation and windage. The rear sight windage adjustment is adjusted by using a screw driver on two screws.
The top screw is loosen to allow for adjustment and then the screw on the right is turned to move the sight. 1 full turn moves the impact 6 inches at 100m. Tighten the top screw back down after adjusting to lock the sight back into place.
Inside the drum there are two tabs. Compressing both tabs inwards allows for the drum to turn adjusting the elevation of the rear sight. You need to turn the elevation drum in 1/4 turn increments for 1.5 inch adjustment at 100m.
If you don’t have the proper HK rear sight tool, a pair of needle nose pliers can be used.
These sights can be annoying to zero, but they are fun to use. But if I was going to be shooting any sort of competition or precision I’d rather use A2 sights with their smaller peep aperture and simpler easier tool less adjustments.