there is room for rounding and estimates, within the confines of "the math".

I track my blackjack play by rounds played, rather than hours or whatever other players (even AP's do). Because rounds played is actually what matters. What the fuck is an hours play anyway? I have been at slow moving crowded tables, (frequently on weekends) that average 40 rounds and hour. And I have played heads up where you can get 300 rounds an hour. So an hours play has NO meaning. It is rounds played that matter.

But I don't sit there and count the rounds played. I estimate. Using things like 2.7 cards per hand, per player and dealer, divided into the number of cards played from the shoe. Pretty easy calculation. But still just an estimate.