These tools provide a quick way to calculate rates that applied on a given date – select the date and the number of weight steps you want (and for airmail the zone) and click the "Show" button.
The display will update itself automatically when you change one of the selections.
You'll get a list of rates for each weight step (up to any weight limit there may have been) for the main types of mail, and for letter mail further columns giving the total rates when additional services were used, where available (registration, express/special delivery, and recorded delivery). A blank square means that the weight/service in question was not available at that time.
Please let the website administrator know if you spot any errors.