Errors Not Revealed by the Trial Balance (COPROC)
Six types of error leave the trial balance in balance but result in incorrect accounts. The mnemonic COPROC covers them all.
The Six COPROC Errors
1. Error of Commission
A transaction is posted to the correct type of account but the wrong personal account.
- Example: £400 received from P. Smith posted to the account of J. Smith
- TB effect: none — total debits and credits unaffected
- Journal correction: DR P. Smith £400 / CR J. Smith £400
2. Error of Omission
A transaction is completely omitted from the books — neither side is recorded.
- Example: a £600 purchase invoice is never entered
- TB effect: none — both sides missing equally
- Journal correction: make the full correct entry (DR Purchases £600 / CR Trade Payables £600)
3. Error of Principle
A transaction is posted to the wrong class of account — usually capital/revenue confusion.
- Example: purchase of machinery £3,000 debited to Purchases instead of Machinery
- TB effect: none — a debit appears on both sides
- Journal correction: DR Machinery £3,000 / CR Purchases £3,000
4. Error of Reversal
The correct accounts are used and the correct amount is posted, but the entries are on the wrong sides (DR and CR swapped).
- Example: rent received of £1,200 — DR Rent Received £1,200 / CR Bank £1,200 (should be reversed)
- TB effect: none — one DR and one CR still exist, same amounts
- Journal correction: double the original amount on both sides
- DR Bank £2,400 / CR Rent Received £2,400
- (This cancels the wrong entry and makes the correct one in a single step)
5. Error of Original Entry
The correct accounts are used and the entry is on the correct sides, but the wrong amount is used — usually a transposition error.
- Example: insurance paid £350 entered as £530 on both sides
- TB effect: none — same wrong amount debited and credited
- Journal correction: the difference only
- DR Bank £180 / CR Insurance £180 (reduces insurance and increases bank by the difference)
6. Compensating Error
Two or more errors cancel each other out — one error overstates DR by the same amount that another error overstates CR.
- Example: wages account overcast by £200 (DR overstated by £200) AND sales account overcast by £200 (CR overstated by £200)
- TB effect: none — the excess on each side is equal
- Correction: correct each individual error separately
Journal Entry Format
General Journal
Date | Account | DR £ | CR £
| Account being debited | X |
| Account being credited | | X
Narration: [brief explanation of the correction]