If I run

select current_date, extract(weekday from CURRENT_DATE) from rdb$database;

I get (note I'm in the UK, so dates are dd/mm/yyyy)

21/09/2006, 4

but the book says

"weekday extracts the day of the week (having Sunday = 1, Monday = 2,
and so on" - which would make thursday return 5.

Have I made a mistake or found a typo (it's not on my type list) ?