The equation for an individual game/console is the following (based on what I remember, and taking into account how things seem to work)
Max(0, 100 - ((difference / actual) * 100))
The accuracy for a single round is then the average of all the games/consoles, so just the sum / 15. (10 games + 5 consoles).
The accuracy I show is the average of the rounds. So If you've been in 10 rounds, then sum all 10 accuracies, and divide by 10. This is the same as if you were to take the average of the accuracies of each individual game/console because each one is weighted the same.