I have 2 free apps on my phone. "County" let's me set how many row repeats is in a pattern (which would work great for a 20 row pattern that repeats over and over) it also tells you how many repeats you've finished or are on - you choose.
The other one, Tallybee, just counts. All you do is tap it. I use it when I'm just repeating one row and I want to know how many I've done for a specific length.