And I've discovered that my Zerofill routine, which can be given any number of leading zeroes, never gets called with anything other than 2 leading zeroes. I discovered that by changing 'watch "Zerofill"' to 'watch "Zerofill." & nWidth'. Zerofill gets called > 700,000 times in a session.
So I create a new version of Zerofill
which I call Zerofill2
and get a slight speed-up