date: date serial value
method: numbering system, defaults to 1
The WEEKDAY function returns the day-of-week of date. The value of method determines how days are numbered; it defaults to 1.
If method is 1, then Sunday is 1, Monday is 2, etc. If method is 2, then Monday is 1, Tuesday is 2, etc. If method is 3, then Monday is 0, Tuesday is 1, etc.
This function is Excel compatible.