Tap the value of each arrow as you shoot and this keeps the running total, your Xs and 10s, and how far through the round you are — the way scorers count at the line.
X counts as 10 and is tracked separately for tie-breaks. M is a miss (worth 0). A WA 720 round is 72 arrows at 70 m — a perfect score is 720 (plus any inner-10 Xs you care to count).