With default tweaks, the number 1 corresponds to Sunday and the number 7 corresponds to Saturday.
The CHOOSE function simply maps numbers to values.
The first argument is the number to map, and subsequent arguments represent associated values.
With a date from column B, WEEKDAY returns a number which is fed to the CHOOSE function.
CHOOSE returns the value at that position in the list of abbreviations.
By default, WEEKDAY returns 1 for Sunday and 7 for Saturday, but this is configurable.
The values provided to CHOOSE can include references.
