Nice chart.... Can someone help me understand what it means?

I shoot an old PSE Edge 1000 lefty bow (65#, 30" draw). I shoot 31" Easton XX-75' s, size #2315 with 125 gr tips.

I entered in #2315 into all the fields, 4" fletching, 3 fletchings, 31" arrow length, and so on, and so on, and it came up with these figures:

Arrow weight: 557grn
Calculate FOC: 10.5%

......' Splain, Lucy!

Butch