You have an obsolete finger
We are all told we use the the base 10 number system because we have 10 fingers. Weird, as we never use the number '10'.
It probably comes from the Roman numerals as by the time 30 was written 'XXX'. But now the number '10' is obsolete as of Arabic numerals, so is you finger I guess. :)<p># don't try to correct this at home