The Edwards perpetual calendar was proposed by Willard Eldridge Edwards in 1943. Dr. Edwards claimed that he had worked his plan out as a student in 1918-1919. It resembles the World Calendar of Elisabeth Achelis in having 91-day quarters containing one 31-day month and two 30-day months, with one intercalary day (after the last day) in normal years and two (after the last day of June and the last day of the year) in leap years, not assigned a day of the week or a month and date, to make it perpetual. The differences are in details:
In the World Calendar, the 31-day month is the first month of each quarter, namely January, April, July, and October. In the Edwards perpetual calendar, the 31-day month is the third month of each quarter, namely March, June, September, and December.
Years in the World Calendar begin on Sunday; years in the Edwards perpetual calendar on Monday.
Edwards suggested the mnemonic "30-30-31; Monday-Wednesday-Friday" for the quarterly pattern. This gives the lengths and first days of the week of the three months in each quarter.
Most of the advantages and disadvantages of the Edwards perpetual calendar are identical to those of the World Calendar, however, some people may prefer to have the years begin on Sunday, the first day of the week, and others on Monday, the first day of the business week; also, since Monday, Wednesday, and Friday are often grouped together, the Edwards mnemonic can make it easier to memorize the calendar.