Arne has a good point, but from the description, I'm not sure the measurement was made correctly. What you should do is to identify the point where the riser section ends and the working limbs begin. This is called the fade-out. On a one piece bow, looking at the side of the limbs, you should be able to see 4 or so laminations in the working part of the limb that extend all the way to the limb tips. On the riser side of that, there will either be more laminations or a solid piece of wood, and an identifiable spot where they meet. That is where you want to make your measurement, which generally shows 1/4 - 3/8" more on the upper limb that the lower limb for split, or possibly less or an equal measurement for 3 under, but as Arne says, generally not negative.