Horrible – FingerMath ABACUS - addition,subtraction Review

There is a mistake in the first few problems. The abacus does not allow you to move on until you sole a problem correctly. Well, if THIER answer is wrong, what are you supposed to do? just keep guessing. Worthless until you fix this. I would like a refund.
Review by Arbeiten on FingerMath ABACUS - addition,subtraction.