@DOW

@DOW[mm-dd-yy]:  Returns the first three characters of the day of the week 
for the specified date ("Mon", "Tue", "Wed", etc.). 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.