MGR/I=21 is BS. When I showed the latest mgr/i value for the current top players (not the Jura data from 2007) the cluster was at 20.0. Travlerajm came back with the silly concept of wrists bands to try to make believe the players are still currently playing with 21.0 set up when the weight of the wrist bands are taken into account. I'm not making this stuff up, there really is a thread somewhere with sweat bands and lower mgr/i of current pros trying to be linked to mgr=21!
MGR/I is the polarization of the frame. Today's pros (men and women) prefer higher SW relative to static weight (polarized), decreasing mgr/i. But pros don't care about maths, they care about winning. And current top players win with low mgr/i. Because that's how you achieve big power and big spin from the baseline. That's what's winning right now.
Now mgr/i is not useless, it's a nice way to gauge the polarization and figure out your set up. But because Thiem, Nadal or Serena have mgr/i=20 doesn't mean you should use that yourself. But because Rod Laver, Lendl and Agassi had mgr/i=21 doesn't mean you should aim for that either.
This thread has been taken over by the mgr/i religion, I hope it will be back to the Ultra Tour quickly.