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.
Basically, the spreadsheet programs store every date as an integer, starts with 1 represents 01/01/1900 and so on. With this system, they can add, subtract, or compare dates just like any other numbers, and all dates are manipulated by using this system. And they also knows how long is every month and which years are leap years.
There is a leap year every year whose number is perfectly divisible by four – except for years which are both divisible by 100 and not divisible by 400. It is not so difficult, is it?
The latest date allowed for calculation is 31/12/9999 in Excel. It won't be so soon. :)
The OpenOffice/LibreOffice Calc is better then Excel in this case, Clac is able to return valid results before 01/01/1900 (using negative numbers to store). The Calc also knows that 15/10/1582 was Friday and the previous day was 04/10/1582 (Thursday of course). Yes, it is so smart.
And we are smarter then these spreadsheet software, because we can use them. Let’s see how! In this case everything is about the formatting.
Enter a real date to the A1 cell and enter a formula to the A2 to be equal to A1. After then we have to format the A2 cell to show the name of the day. That’s all.
I made two short tutorial about the steps, the first one shows Hungarian Microsoft Office Excel 2010, the second one shows English LibreOffice Calc 4.0. And just for the record, in Hungary we prefer the YYYY/MM/DD format then DD/MM/YYYY.
When you see the green button with an arrow, you can click on it to continue, and when you see the green button with two white squares, you can click on it to repeat.
Excel (Hungarian): http://lengyelke.com/wink/oroknaptar.htm
Calc (English): http://lengyelke.com/wink/oroknaptarlibre.htm