Question with primary arms 6x magnifier

[baekacaek]

I just got a 6x red dot magnifier from primary arms. Its great and I have no problems with it so far; wish that it had longer eye relief though. I noticed that the eye piece has "+" in one direction and "-" in another, and is seemingly rotatable infinitely. I can't seem to figure out what rotating the eye piece does. Can anyone with experience explain? Thanks!

[essjay]

Focus ring to adjust for eye relief?

[JMP]

I'd assume this is a diopter adjustment. When you are looking through your sight + magnifier, you may find that you will want to rotate it for optimal clarity of your reticle based on your eye.

[PrimaryArms]

Correct please read the instruction and focus it for your eye.

[Merc1138]