This is a little game you can play to test how well you know an exercise or piece of music. It's also a great test of your attention to detail, the depth of your analysis and self-criticism, and most importantly, your patience. Impatience is the aspiring musician's greatest enemy.
It works by dividing up the exercise/music into individual phrases, or any suitably sized chunks, and then playing those individual bits accurately 20 times over. If you play all 20 repetitions perfectly, you move on to the next chunk. If you get one wrong, rather than starting again from scratch, you simply go back 1 to the previous number. For example, if you've done 10 successful repetitions, and you mess up the 11th, you go back to 9.
So it might go something like this: correct repetition "1", correct repetition "2", correct repetition "3", correct repetition "4", incorrect repetition "3", correct repetition "4", correct repetition "5", incorrect repetition "4", correct repetition "5" etc, until you manage to get to 20.
You can see that by doing it this way, you could get up to 5 or 6 or whatever, then by playing the phrase incorrectly over and over, you could go right back down to 1, and beyond. This is where the honest analysis, self-criticism, and of course patience comes in; all really useful habits.
What happens if we go beyond 1? Well, you first go to 0, this is your last chance to stay in the game. If you mess up again, you go to -1. If you enter negative numbers, you're out, so you halve the time, and begin the game again, seeing if you can do 10 accurate repetitions; half as many because it takes twice as long, and is twice as easy. For example, if you were playing 16th notes at 100bpm, you simply leave the drum track/metronome alone and play in 8ths instead. If you can't pass at half speed, then you either don't know the music well enough, or lack the general technical ability to play it. This is a good thing to know, and is the purpose of the exercise. Practice is about finding weaknesses not showing off strengths.
And that's about it. There isn't much more to say. It seems silly to post an article this short, but I believe the game is really useful. It just doesn't require a lot of explaining.