Spine of the actual arrow is the fourth. One needs to purchase an arrow that will be condusive to shooting well with the draw length, head weight, and poundage that one plans to shoot and tune from there using the 3 remaining factors. First, determine the length of arrow that best fits your set-up (I like just over an inch in front of the rest). Then determine the draw weight of your bow (it's best to start near or at max for your bow). Choose the weight of broadhead that you will use (100 gr. is generally the standard today). Now you begin to tune the bow to your arrow by moving the rest laterally and adjusting the draw weight to achieve perfect paper tuning flight. There is no reason to have an arrow protruding 6" in front of your rest. Set things up right the first time and you won't have to fight with your bow so much.
