The Wealth of Nations by Part 1 Chapter 11 Page 114

happen to be the price of the fiars of each year, than at any certain fixed price. But the writers who have collected the prices of corn in ancient times seem frequently to have mistaken what is called in Scotland the conversion price for the actual market price. Fleetwood acknowledges, upon one occasion, that he had made this mistake. As he wrote his book, however, for a particular purpose, he does not think proper to make this acknowledgment till after transcribing this conversion price fifteen times. The price is eight shillings the quarter of wheat. This sum in 1423, the year at which he begins with it, contained the same quantity of silver as sixteen shillings of our present money.

But in 1562, the year at which he ends with it, it contained no more than the same nominal sum does at present.