I'm not sure how well I can explain it, but I'll try.

It's similar to a scope on a rifle, except that you don't look *through* it. You just look *at* it. When you look at it *right*, there are rings like a bullseye. The idea is to line up the rings perfectly. If you don't look through a scope just right, you see 'black' around the edges. If the No-Peep isn't set just right - or, rather, if your eye isn't in the perfect spot (your proper anchor point) - you won't see the rings in it.

So, you set it up so that when you draw back and anchor properly you glance at it and you see the rings line up like a bullseye. If you are torquing your wrist or you have the anchor point wrong, you won't see the rings show up on the No-Peep. It's ultra-sensitive and works very well, IMO.

Hope that helps.