How do you know what day of the week was October 13 1972?

Answer 1

One way that I determine the weekday of a particular date is to enter the date into a cell in a Microsoft Excel spreadsheet and to format the cell to show the weekday. For dates before 1 January 1900 I add a multiple of 400 to the year to make the year greater than 1899 (the Gregorian calendar completely repeats itself every 400 years).

The other way is to look at the year in the perpetual calendar I created for myself.