To determine which way my ball will break I use the little dots/balls on the grid. When the grid comes up be sure and wait. Watch how fast it takes a dot to appear and then cross one square of the grid in the intended path of your shot. I have noticed that sometimes it takes a few seconds for them to get in 'flow' mode. How much to adjust for is a judgement call at that point.
Keep in mind that if you put too much power behind the ball it will effect roll as well. Too much power doesn't necessarily mean that it won't go in the cup but it does effect roll. It is important to learn to judge precisely how much power is needed to reach the cup. That takes practice, lots of practice!
The inches up or down is as Petebolte stated. It is exponential. Don't give them as much weight in your judgement when the ball is three feet from the hole. From twenty five feet the ball is losing speed as it approaches the cup. That three inch rise will make a difference for sure!
Just in the real game it all comes down to practice. There is a practice option. Use it. When I play the practice course I usually end up with the maximum strokes on a hole. That's because I'm experimenting with power, aim,and clubs.
I hope someone finds this info useful.
Glhad