Errors sometimes occur when recording accounting events. To rectify errors, a new correcting entry must be made rather than altering the original incorrect entry. There are several types of errors, including errors of omission (leaving out entries entirely), errors of commission (recording entries incorrectly), errors of principle (incorrectly classifying items), and compensating errors (errors that offset each other). Errors can affect the trial balance if they involve incorrect totals, balances, or postings, but some errors like incomplete omissions or wrong original entries do not affect the trial balance. Errors must be rectified when discovered, whether before or after preparing financial statements.