The invention of double-entry bookkeeping has had profound implications on our world. All modern commerce owes a debt (hi!) to it. I have heard it compared to the invention of numbers. In turn, this accounting mechanism was made possible by the sudden availability of cheap paper. In The notebook: a history of thinking on paper, Roland Allen writes: Before paper became easily available in the years after 1244, Italian merchants had used parchment books to record their transactions, but they recognised a superior product when the first paper ledgers arrived. Ink dries on the surface of parchment, but soaks into a paper sheet. This makes it a permanent medium, whereas parchment, which can be scraped clean and written on again, allows records to be revised after the event—opening the door to fraud. Accounts were always bound into ledgers for a similar reason: loose-leaf entries could easily be fabricated, but a ledger with numbered pages became tamper-proof. This in turn meant that merchants could delegate to subordinates or branch offices without fear of embezzlement, allowing traders to widen the circle of their businesses. Purchases, sales, loans and terms of business were no longer recorded inconsistently on a scrap of easily rewritten parchment: they were carefully entered into a permanent record that, in the event of dispute, was accepted as evidence in a court of law.