As an example, some idiot (it's easily done) posts a credit entry as debit. All error corrections are posted to the Journal A/C, usually situated in the General Ledger, with the corresponding double entry in the A/Cs which contain the errors.

To correct the error without taking the Journal into account, one post restores the A/C to its original balance prior to the error, then another entry is required to kick the balance into its correct value. If the error originally occurred in a memorandum account, the error will trickle down to the General Ledger, so another couple of entries are required.

I think that a reverse error entry in the Sales or Purchase Ledgers that is discovered after the end of the financial period requires eight entries to correct it.

In theory some compound errors may require dozens of entries to correct.