@DATE

@DATE[mm-dd-yy]:  Returns the number of days since January 1, 1980 for the 
specified date.  DATE uses the date format and separators mandated by your 
country code (for example dd.mm.yy in Germany, or yy-mm-dd in Japan).  The 
year can be entered as a 4-digit or 2-digit value.  Two-digit years 
between 80 and 99 are interpreted as 1980 - 1999; values between 00 and 79 
are interpreted as 2000 - 2079.