The correct AMO arrow length is 1 inch in front of where the arrow contacts the rest. And this is where most charts and online calculators are going to calculate spine from. This is also the point you would measure brace height and power stroke from. You will notice they either ask for draw length, or arrow length not both. So they (arrow charts) just assume you are using the correct arrow length for your draw length. If you are not you need to know how to fudge the numbers some. It will still get you fairly close though. And remember the arrow charts and online calculators are just estimated guesses to get close. They don't ask any where near enough information to be accurate.

The problem is this was based on people using conventional prong type rests set up correctly. Which would put the contact point of the arrow and the prongs right above your grip. Many of the newer rest actually set up behind shelf and work as a slight overdraw and the contact point could be 2 inches or more behind where it really should be. If you followed the rule of one inch beyond the contact point of the rest you would end up with shorter arrows than you really need.

AMO draw length is figured by measuring your power stroke or "true draw" and then adding 1.75 inches to that number. Basically just nock a full length arrow ( or one that you know is longer than your draw length), then draw the bow back and have someone mark the arrow right above your grip. Then measure the length from the nock grove to the end of the shaft (not the tip if one is installed!). This is your true draw or power stroke. Add an inch and 3 quarters to that length (1.75") and that is your AMO draw length.

So basically you can just cut your arrows 3/4 of inch shorter than your draw length as long as you know your draw length is correct. A lot of people just cut their arrows the same length as their draw length to cut down on confusion. In most cases 3/4 of an inch isn't going to make a huge deal. Unless you were close on being under spined or something.

A shorter than needed arrow will be stiffer in spine and weigh slightly less, a longer than normal arrow will be weaker in spine and weigh more.

Your actual arrow length really doesn't matter as long you match the spine correctly. Someone that is really familiar with certain arrows and the spine charts might be able to this, or there is software available that figures it for you. I use Ontraget2, it lets me enter any length arrow I want and it will tell me what sizes will work at that length. I shoot a longer than needed arrow.

There are advantages and disadvantages to shooting shorter or longer arrows than needed. It would depend on your needs and what you wanted to do.

Paul