Those charts are only a ball park figure and IMHO they are totallymissleading.

I had a gentleman pm me yesterday about his set up 70lb, 27.5" draw and 27" arrow (5575),when I ran his numbers the spine was weak.

I suggest that if the chart say's you need a 5575 (400 spine) arrow go to the next stiffest.

This is one of the reason most people have trouble tuning their bows.