Manufacturers for games up through the mid to late 70s recommended 3-1/2
degrees of playfield angle. Since then they have gone to a steeper
recommendation of 7 degrees. On a flat surface, with leg levelers all even,
all machines should be fairly close to the recommended angle.
Now, the real scoop on playfield angle. If your game seems too slow or too
easy, increase the pitch. If it's too fast and too hard, decrease the
pitch. That's all there is to it. I've found some games play better very
steep, and others are more fun with a very gentle slope.