It also depends on where in the string youi needed your peep to end up to give you proper alignment... if you slide the peep up and down the string after it's inserted into the string, you'll notice that it will turn as it moves along -- because the string is twisted together.

Sometimes that means that your peep ends up in a spot where -- after shooting your string in with 50-100 shots or so -- you'll need to put your bow in a press and add or remove a twist to move your peep so that it's in the position you need it to be. Once you get it right though you shouldn't ever have to move it again.