WAY BACK in 1991
... Later that day, I had some time, so I started working on figuring out if Basic had enough date and time functions to do all the things you could do in Excel.
In most modern programming environments, dates are stored as real numbers. The integer part of the number is the number of days since some agreed-upon date in the past, called the epoch. In Excel, today's date, June 16, 2006, is stored as 38884, counting days where January 1st, 1900 is 1.
I started working through the various date and time functions in Basic and the date and time functions in Excel, trying things out, when I noticed something strange in the Visual Basic documentation: Basic uses December 31, 1899 as the epoch instead of January 1, 1900, but for some reason, today's date was the same in Excel as it was in Basic.
I went to find an Excel developer who was old enough to remember why. Ed Fries seemed to know the answer. ... http://www.joelonsoftware.com/items/2006/06/16.html