There’s a misconception about snooker tables that they must be perfectly level. Whilst a good fitter will always get the table as level as possible, you should note the expression used by fitters is “to level table to best advantage”. This is because a perfectly level set of slates is quite a rare thing – if you spend enough time slowly rolling balls all around a snooker table the odds are you will find an area with a small amount of “drift”. This is not just down to the slate but also the cloth as different areas wear at dissimilar rates – the black spot end gets more use, so gets more finger, scuffs and tracking marks. New cloths can also cause minor movement due to the finishing process.
The nap of the cloth which runs from the Baulk or D end of the table also plays a part, balls going against the nap from the black end to the baulk end when played slowly will drift slightly, a pink potted into the yellow pocket will drift to the left – so on a slow shot aim for the inner jaw of the pocket. A pink potted into the green pocket will drift right so again aim for the inner jaw. It’s the same with potting a ball from the pink spot area – aim at the far jaws.
I should point out this only happens at slow speed and modern cloths have very fine naps, some of the older heavier napped cloths could roll several inches when played slowly against the nap of the cloth.
Incidentally this is why potting a ball along the baulk cushion is harder than potting a ball along the black spot end cushion as the nap can push the ball away from the baulk cushion. At the black end the nap helps the ball stick to the cushion. If you run your hand down the table from the D end to the black spot, the cloth will feel smooth, run your hand the other way you will feel the nap of the cloth a bit like dralon. This is assuming the cloth is not completely worn out of course!