why is the vendor number written in the post. ref. column of the purchases journal?

The vendor number is written in the Post. Ref. column of the purchases journal to provide an audit trail back to the specific vendor account where the transaction was posted.

What the Post. Ref. column does

• The Post. Ref. (Posting Reference) column is used to show where a journal entry has been posted in the ledger system.

• Writing the vendor number there links the purchase entry in the purchases journal to the correct accounts payable (vendor) ledger account.

Why the vendor number is used

• Using the vendor number in that column creates a clear audit trail, so anyone can trace the transaction from the journal to the vendor’s ledger account and back again.

• It helps prevent errors (like posting to the wrong vendor) and makes it faster to check balances, investigate disputes, or answer questions about a specific invoice.

How this looks in practice

• In a typical purchases journal, you see details like date, vendor name, invoice number, and amount; the Post. Ref. column will then contain the vendor number once the posting into the subsidiary ledger is done.

• When reviewing the vendor’s account in the accounts payable ledger, there will usually be a matching reference back to the purchases journal entry, completing the two‑way link for control and verification.

TL;DR: The vendor number goes in the Post. Ref. column so that every purchase on credit can be traced directly to the exact vendor account it was posted to, forming a reliable audit trail.