How do Casino's track your cumlative win/loss??

If I just take my chips and walk away from the table during a shuffle, rathole chips any number of ways, how do casino's tell my cumlative win/loss?

Lets say I buy in for $100 at a table, am down to roughly $75 during a shuffle, and just walk away, take a break, get lost for a bit, and stuff the chips into my pocket. Then, 10-15 minutes later I walk to a new pit, buy in for another $100, and keep doing this throughout the session. Does the casino think I've lost $100 at each table? How do they estimate my win/loss? Does the 'eye' keep count or do the pit staff just keep track, etc.

J.