Double-entry bookkeeping 2: books of prime entry, accounting systems
. A complete reversal of entries error occurs when two or more errors cancel each other out.

. An error of principle occurs when a transaction is posted to the wrong type of account.

. When a transaction is posted to the correct type of account, but the wrong account is debited or credited, then an error of omission has occurred.

. Transposition errors are always divisible exactly by 9.

. Even when errors are made in the posting of the T accounts, the trial balance will still balance except when a transposition error occurs.