The world, of course, didn't begin on January 1, 1900. People who work with historical information when using Excel often need to work with dates before January 1, 1900. Unfortunately, the only way to work with pre-1900 dates is to enter the date into a cell as text. For example, you can enter the following into a cell, and Excel won't complain:
July 4, 1776
You can't, however, perform any manipulation on dates that are actually text. For example, you can't change its formatting, you can't determine which day of the week this date occurred on, and you can't calculate the date that occurs seven days later.
The companion CD-ROM contains an add-in that I developed called Extended Date Functions. When this add-in is installed, you have access to eight new worksheet functions that let you work with any date in the years 0100 through 9999. Figure 3-8 shows a worksheet that uses these functions to calculate the number of days between various pre-1900 dates.
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