Check my math here on draw weight....

[highpoint forge]

74# @31 is 67 @28" correct? 64AMO bow does not factor in, just the weight at draw IIRC....

[wingnut]

Depends on the bow and the bow length.  Could be stacking at 31" and gaining 5+#s per inch.

Mike

[NY Yankee]

3lb per inch is just an average guess. You could be getting more weight from 30 to 31". Only right way to tell is a scale.