The Wealth of Nations by Part 1 Chapter 11 Page 143

From 1595 to 1620, both inclusive, the average price of the quarter of nine bushels of the best wheat at Windsor market appears, from the accounts of Eton College, to have been L2 1s. 6 3/4d. From which sum, neglecting the fraction, and deducting a ninth, or 4s. 7 1., the price of the quarter of eight bushels comes out to have been L1 16s. 10 2/3d. And from this sum, neglecting likewise the fraction, and deducting a ninth, or 4s. 1d., for the difference between the price of the best wheat and that of the middle wheat, the price of the middle wheat comes out to have been about L1 12s. 9d., or about six ounces and one-third of an ounce of silver.

From 1621 to 1636, both inclusive, the average price of the same measure of the best wheat at the same market appears, from the same accounts, to have been L2 10s.