Have you ever wanted to know what day of the week is your birthday? If you liked to know you should use a perpetual calendar. When I was child, I used a special table printed on paper, but nowadays we can perfectly do it with a spreadsheet program. There are some advantages and disadvantages to both of them. Maybe the most important is the range of the dates the calendar can work properly. The printed version is up to the authors’ skills. If you wanted to use a spreadsheet software, you are supposed to know the earliest and the latest date allowed for calculation.