"What happens if you move the cart forward?" Assuming that the arm is set to the proper P2S distance, if you move the cart forward the stylus will no longer be tracing the arc at the correct effective length and your alignment will be off.
Think about what the overhang distance is, what the P2S distance is, and how they relate. If you do so you will realize that these vectors are incorporated in the radius used to draw the arc on your protractor. So if you set the stylus to the arc, overhang for that cart on that arm are set correctly. Don't get hung up on where the screws end up.
Think about what the overhang distance is, what the P2S distance is, and how they relate. If you do so you will realize that these vectors are incorporated in the radius used to draw the arc on your protractor. So if you set the stylus to the arc, overhang for that cart on that arm are set correctly. Don't get hung up on where the screws end up.