IIRC you take your bow weight and subtract/add 10 lbs. of spine for every inch of draw, then add 10 lbs. for the broadhead.
IE. 27" would be 40lbs., then back up to 50 lbs. for your broad head.
Then add and other 10 lbs because you ant to shoot an 1" longer arrow.
For arrow weight, use 100 grains of arrow for every 1lb. of bow draw, then add 100 for the broad head, and another "just because".
I like to shoot HEAVY arrows!
However, Ii have seen different systems as well....