I've been comparing BTM vs. BJI numbers for years.
My basic conclusion is that numbers are good ONLY within any one system, if that. Comparing BTM to BB.com or BJI to BTM is fruitless and fraught with peril. You're much better off trying to extract information based on the words used to describe the ball than the numbers generated by any one source.
Look at the reasons behind the numbers:
- what kind of bowler is doing the testing for what purpose?
- how is the ball drilled? For generic use, for maximum hook, for maximum backend, for minimum hook?
- what surface did they test in what oil patterns, to what end?
Many times, the testers don't even know what the ball is designed to do.
BTM puts the best (not necessarily the strongest) drilling for each of their testers: stroker, tweener, cranker. What BB.com does I don't know.
BJI puts a generic drilling on theirs.