Where should I measure for the length of the body and the sleeve. I have made sweaters before and I always seem to either want it longer or shorter than the finished sweater. The one I am working on now says work to 13" then shape for arm holes. Should I measure right up under my armpits or one inch down or where. The same goes for the sleeves. I know some sweaters have a bigger drop in the arm pit area. So how do I know for sure where it will end up.