Have a look at the following link...

http://www.mcgimpsey.com/excel/formulae/doubleneg.html

Cheers!

In article ,
ArthurN wrote:

Hi,
I saw this formula:
=SUMPRODUCT(--(A2:A65536<""),--(B2:B65536=""))
And I have no idea what "--" means, I tried searching the manual and the
internet but found nothing.
ArthurN