A more thorough explanation:

Definition: Mensura domini regis was a set of standard weights and measures established by King Richard I in 1197. It was decided that there would be only one weight and one measure throughout the kingdom, and certain people in every city and borough were responsible for keeping the standards. These original standards were called pondus regis and mensura domini regis. They were kept in the exchequer, and all weights and measures were required to be made conformable to them. Example: If you go to a store and buy a pound of apples, you expect to get the same amount of apples as you would at any other store. This is because of mensura domini regis, which established a standard weight for a pound. The same goes for other measurements like feet, gallons, and bushels. This helps ensure fairness and consistency in trade throughout the kingdom.