I've often felt that pulling a bowstring by a scale with a small hook isn't really the same as pulling it with three fingers. If you draw the bow to, say, 26" using three fingers with an arrow in between, then you've got about 2.5" of bowstring at 26". If you pull the same bow using a scale hook, only about 1/8" of string is at 26". The rest is at an angle toward the tips, effectively shortening the draw. Therefore, the actual draw weight using fingers should be slightly higher than that measured with a scale.
I couldn't convince myself on paper whether or not this difference would be negligible, so I did a quick experiment. I cut a 2.5" piece of PVC to simulate my fingers, and put a bowstring through it. I then drew the bow to various lengths using: just the scale hook; and using the hook attached to the PVC. Low and behold, the weight was measurable larger using the PVC. On this particular bow (which pulls around 60# @ 24"), there was a 1 1/4# difference at 23" (give or take a few ounces due to my imprecise setup).
I found that if my bow is drawn to 23 1/2" using just the scale hook, it gives the same reading as drawing it to 23" with the simulated fingers. Therefore, the bow hook underdraws the bow by more than 1/2" when approaching full draw. This could amount to a 2-3# discrepancy or more, depending on bow length, draw length and bow weight.
Thoughts?
