One very fast way I found the center shot is.
1. A piece of bright colored thread.
2. Allen bits that fit your limb pockets.
3. A bow square.
First place the Thread over the hole in the limb bolt. (thread hanging down in line with the riser)
Second place the the Allen bit in the hole.
Third pull the thread tight and lay across the bottom limb bolt
Forth place the Allen bit in the bottom limb bolt (make sure the thread lines up with the end splits in the limbs)
Now you are ready to put the bow square on the string. Line up the bow square with the thread and place a piece of tape on the riser, where the center is. You can also eyeball the sight and line it up too!