In 1540 a Venetianprinter named Domenico Manzoni excerpted them, without attribution(Pacioli himself had acknowledged most, but not all, of his sources) butusefully adding hundreds of worked examples which illustrated Pacioli’spoints. Tellingly, Manzoni retitled the work Quaderno Doppio, ‘the doubleledger’. Selling even better than Maestro Luca’s original, it went throughsix or seven editions and prompted a wave of adaptations and translations.

of the six hundred pagesof the Summa, only twenty-seven covered bookkeeping.

In short: Book ix of the Summawas the nearest thing to an MBA textbook that the fifteenth century had tooffer. And one of the first lessons that its aspirational readers digested wasthat every business needed at least four blank books – the memoriale, orday book, the giornale, or journal, the quaderno, or general ledger, and abook for correspondence – and maybe even a fifth, the squartofoglia, or

And buried deep inside,Book ix of the Summa presents a concise and surprisingly readable coursein double-entry bookkeeping, spelling out exactly how a business should berun – and why the Florentine-Venetian system of double entry was the bestway to do it. ‘Without double entry, businessmen would not sleep easily atnight’, he writes. ‘Their minds would keep them awake with worry.’