function WeekDayOf(Value: DateTime; UTC: Boolean=False): Integer
The WeekDayOf function returns the week day number of the input parameter in local or UTC time. This function is ISO 8601-compliant, meaning that the week days of Monday through Sunday are represented by the values 1 through 7, respectively. The return value is an Integer value.
Examples
X := WeekDayOf(Date); // X is 1 (Monday, assuming a date of 02/13/2012)