Out of this extraordinary tax evolved a system, overseen by Roger of Salisbury, the name of which survives as the centre of British government finances today: the Exchequer, so-called because the moneys due to the crown in Henry’s time – rents, taxes and fines – were laid out on a large table. It was ten feet by five, with a three-inch rim around its edge to stop anything from falling off. This counting table was covered with a cloth, on which there was a pattern of horizontal and vertical squares, as would be found on a board for a game of chequers. The columns of squares had different values, starting with pennies, progressing through shillings to pounds, all the way up to tens of thousands of pounds. The royal accountant set out counters across the top row of squares, representing the sums that he had calculated as being due to the crown. Along the row immediately below this were laid out further counters, showing what had actually been paid in against the debt. In an age of complicating Roman numerals, the employment of what was, in essence, a giant chequerboard abacus reduced payments and debts to their simplest and most digestible form.
Charles Spencer in The White Ship