Ok, if casino is using say 20 and 18 mm balls. What would be the best way to find the difference.?
When the ball is resting inside of the pocket of the pocket i usually can see of the ball is above 18mm or not. But unfortunately you cant choose, so what does it matter? Yes is do matter if you have previous spins saved.
But what would you prefer an 18 mm or a 21? An 21mm retards faster so the ms difference between spins are higher. But that one has higher CG and can easier climb over pockets.
18 mm Teflon/Ivorine and 21mm Teflon/Ivorine
There is a very small difference in size of two balls, as 19 and 20 mm. But a bit larger one can provide some advantage. I can spot the difference only when they are on two tables next to each other.