There are different ideas. Bowyers also think differently. When you find your "sweet spot" you can measure from any point you choose. I measure mine from the deepest part of the grip to the string. My bowyer measures from the handles edge. I use the same dimension that he does which makes my fistmill somewhat less than what he uses. But that's fine, my bows all shoot really well there. Some bows need more, some less. People's releases also differ. The key, find "the spot" and be consistent with your measuring spot.
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All is not equal. Wouldn't be fun if it were.