Severely overspined can give a false weak reading.
Reason is they leave the bow so nock hard right that the tail of the shaft hits the riser kicking it hard left.

Steve

Steve,
Uhhh, No, I just remembered seeing topics on spine, carbon arrows, weird bare-shafting issues, did a few searches, and "Bingo".
It's all these other guys around here who know all this stuff!
Well, come to think of it, I DID stay in a Holiday Inn Express last night...LOL!

I had the same thing with carbons out a 53 pound bow and the same arrows out of a 65 pounder flew straighter, but not as good as cedars.  That to the right hit with a standard longbow for me was the bouncing off the bow.  Also, some longbows don't like three under, The bottom limb is already stronger and shooting three under makes it imbalanced more yet.  I had a three under bow that was tillered for three under and it made a difference.  The only reason I was experimenting with it was, that particular bow was built that way, not the way I ordered it.  I shoot standard.