Seems like these are the GI issue BUIS on the flat topped M16/M4 (and can be used on the civlian AR flat topped rifles as well).
Apologies if this info is somewhere here and I didn't see it.
Matech BUIS Zeroing Instructions
M4/M4A1 Carbine - To zero the M4/M4A Carbine, turn the range knob until the line on the sight cam on the left side is aligned with the 300 meter mark. Use the 25 meter zero target for the M4 Carbine and center your rounds by adjusting the weapon front sight post and BUIS windage adjustment knob.
To zero the M16A4 rifle - To zero the M16A4 Rifle, turn the range knob until the line on the sight cam on the left side is aligned with the white line between the 300 and 400 meter marks. This mark is a half notch location, so it's more difficult to align. Use the 25 meter zero target for the M16A2/M16A4 Rifle and center your rounds by adjusting the weapon front sight post and BUIS windage adjustment knob.
From the sight packaging: