WEEKDAY converts a serial number to a weekday.
This function returns an integer indicating the day of week.
@METHOD indicates the numbering system. It defaults to 1.
For @METHOD=1: Sunday is 1, Monday is 2, etc.
For @METHOD=2: Monday is 1, Tuesday is 2, etc.
For @METHOD=3: Monday is 0, Tuesday is 1, etc.
Note that Gnumeric will perform regular string to serial number conversion for you, so you can enter a date as a string.
This function is Excel compatible.