Originally Posted by Mikecr
I imagine 'R' would be for ranging power setting. As in reticle ranging
If you want to range with the reticule...you need to do it on the "R" zoom power, or know the math to convert it at the rest of the zoom range.
Zooming back down to 11x for example, makes it easy. Your reticle measurement is just 2x what it would normally be at the prescribed "R"
Part of the reason people prefer the 5.5-22x is because you can range at full 22x... 1/2 power (or 11x) and also at 1/4 power (or 5.5x) and it's easy to convert in your head.