There have been several studies of medieval bookkeeping practices. This paper adds to that literature by focusing on the treatment of errors in the ledger of the Medieval Italian merchant, Francesco di Marco Datini, most of which were for the years 1395-6. The analysis shows that, contrary to the perception in the literature, accountants of that period not only detected errors, but also devised methods to address them that ensured that the overall financial result reflected a fair presentation of what had occurred, and that they did not simply use the account for Profits and losses as an easy outlet in which to record an amount that balanced the books. In addition, the accuracy of individual ledger accounts was not deemed important once they had been balanced, even after errors were detected.
Keywords: Ledger, trial balance, operating income, operating loss, the Profits and Losses account, adjustment entries.