With the percession machining of todays bows there is a easy and cheap way of setting the center shot.
You dont need a expensive laser or any other high tech gismo.
This is how I set my center shot.
First I take a large rubber band and place it over the top limb bolt then stretch it to the bottom limb bolt. If your bow does not have the raised Allen head screws insert a Allen wrench in each limb bolt and stretch the band around the wrenches.
Then load a arrow placing it the gap of the rubber band.
If your center shot is off the arrow will push the band to the left or right now adjust the rest so the arrow is in the middle of the band.
Then with that done move onto the next step in the tuning process.
I have been using this method for well over 10 years and it has yet to let me down.