bc,

Think of it this way... When you hang the bow string on a scale, the weight of the bow actually starts the draw. It won't be much but if the bow weights 5# then it will be some. Now imagine hanging a 40# weight on the bow. Now you will have a total of 40# + 5# = 45# pull onthe string and you will clearly see that the bow is now drawn several inches. Your scale would read 45# also. Its reading the weight of the bow plus the additional weight you've added. Nowif you put your hand on the handle and push down to bring the measurement to peak weight (lets assume peak is 70#) you would only need to push down a little bit. Theoretically 25# because 40+5+25=70. Themore weight you hang on the bow, the less you push with your hand to get to peak.

Like I said earlier. Given a typical measurement condition, if you subtract out the weight of the bow the result is the force you exert on the handle but that's not what you're after. You want to know the force to draw the string.

I'm not sure why you're getting a difference when you pull up fro the floor. Is the scale upside down relative to gravity, you put the string on the scales hook and pull up on the bow handle? Off the top of my head the only thing I can think of is maybe there is some slop in the scale that is taken out when it is right side up but not upside down. Not sure but it shouldn't matter what direction you pull. The scale only measure the force applied to it and that is independent of direction. If you attach the string to the fixed scale and pull the bow away or you fix the bow in place and pull the scale away the scale sees only the force between the string and itself.