A continuous record of the books belonging to Francesco di Marco Datini, a merchant of Prato, from 1366 to 1410, shows that Hindu-Arabic numerals began to appear about 1366 and that until 1383 the accounts were kept in narrative form. After that date, however, the practice changed and assets and liabilities began to be kept in parallel columns either on the same page, or on facing pages. From then on it was immediately obvious, as it had not been obvious before, whether a business was in profit or loss.
