Balance the tables whenever they differ by two or more players. The one who moves is the player about to post the big blind, and they take the worst open seat at the other table. Opening or closing a table is different: too many people move at once for the big-blind rule, so the movers are drawn at random and the room evens out as far as it can — 19 across three tables becomes 7, 6 and 6. Merge to one table at eight players and everyone redraws for seats.