Take Art Tatum's solo version of "You Go to My Head" from the Complete Pablo Solo Masterpieces. I'd say it has a different sort of rhythmic elasticity from that of Bud Powell. The part that interests me start at about 1:24, when he settles into a stride groove after the opening rubato section. What's interesting is that there are times when he seems to lose the beat in a series of complex, arhythmic runs and ornaments. But if you were to snap your fingers on 2 and 4 and not stop even when Tatum seems to lose the beat, you will see that he comes out of the runs exactly on time, kind of like an olympic platform diver who enters the water perfectly despite all the twists and turns of the dive itself. He will mark the beat again with a return to the stride left hand, try to get the listener lost again, return again, etc...

For a poor musician like me it's a good excercise to try not to be thrown off by the seemingly rubato sections that are not actually rubato after all. If I can count without losing the beat, instead of trying to follow where I think he is going, I am successful. The two or four to which I'm snapping my fingers might seem to correspond to nothing at all in the music that Tatum is playing, so I have to rely on my unsteady internal metronome.

What happens when I am lost? Basically, it means that I am following the variable and not the constant, confusing the phrasing with the beat.

Repeat the same exercise with a Max Roach drum solo. Hear everything he's doing in relation to the structure of the song he's playing. I wish I could say I can do this with ease.