What's the difference between a Penn 1 tennis ball and a Penn 4?

Question

What's the difference between a Penn 1 tennis ball and a Penn 4?

Answer 1

There's no difference between the balls (except the number).

It's just so that if you bring 3 balls (1 tube) you can know which balls are yours because you have 1 set of numbers

Answer 2

The numbers don't actually mean anything as far as the ball is concerned.  They are only used for identification purposes.  Basically, don't put two cans with the same numbers on consecutive courts, so the players are using the same set of balls the whole time.  My high school would use 1's on court 1, 2's on 2, 3's on 3, 1's on 4, and 2's on 5.  For some reason, we never had anything numbered higher than 3.

Answer 3

The ink