In 1464 King Edward IV instigated changes to the valuation of currency in England. Changes to the valuation of gold and coinage minted from it were economic changes designed to combat problems faced by the treasury, and/ or to stimulate economic growth. In this case, the context was a combination of a bullion shortage, the treasury having depleted stocks of gold, and issues relating to international trade following the change of regime.
An editorial section of the Chronicles of the White Rose of York outlines the changes that were made by King Edward IV in 1464:
In the year of our Lord 1464, this King a.d.1464 Edward, somewhat eased of his enemies, began to have regard unto the redressing of the inconveniences used in the realm for fault of Justice and misordering of money. Wherefore in the latter end of this year he changed his coin. First he made the royal of gold, price 10s.; the half royal, 5s. ; and the fourthing, 2s. 6d. Secondly, he made the noble, and named it the Angel, of the price 6s. Sd. ; with the half of the same, 3s. 4d. Furthermore he made the Groat, the half groat, and pence of less value by 8d. in the ounce than the old groat was. And fine gold was enhanced to 40s. the ounce, and other base gold after the rate, with other divers ordinance of money.
The policy of thus tampering with the coin had always been questionable. William Wyrcester, a contemporary, complains of the injury suffered thereby, particularly by the nobility (p. 500). The author of the [Hearne’s] Fragment makes a mistake respecting the noble. It was raised from 6s. dd. to 8s. 4d. [William Worcester page 500]
Source: Chronicles of the White Rose of York.