RE: Spine adjustment?
Each arrow manufacture has their own standard for measuring spine. Take Beman for example. 340's are stiffer than 400's. You just have to look at a arrow chart. Generally arrows that are stiffer are heavier. This is simply a rule of thumb. +- 2 grains is for the entire arrow. 2 grains means almost nothing, it's not worth worrying about unless you are a target archer that is really really good.