Two frames matched for weight, balance, and swingweight. Strung the same way too. The only difference is that to achieve the desired specs "Frame 12", as we'll call it, has extra mass added at 12. "Frame 39" has extra mass running from roughly just below 3/9 and up towards 2/10. Even with the same SW Frame 12 generated a lot more power (too much really). From 39 didn't feel anywhere close to as powerful. I've read somewhere that mass added towards the top of the hoop can cause a frame to play stiffer. Could that be the reason for the power difference? I should note that that when purchased the frames were matched for balance, weight, etc., and when modified with identical mass placement they play the same.