DATEVALUE
Category: DateTime Function.
Description: Converts a date's text representation into a serial number that represents a date.
Syntax: DATEVALUE(date_text)
For example: =DATEVALUE("22-aug-2008")
Dates are stored as sequential serial numbers to they can be used in calculations.
By default, January 1, 1900 is serial number 1, and August 22, 2008 is serial number 39682 because it is 39,682 days after January 1, 1900.