"JMB" wrote in message
...
David is correct, but the double minus also converts true/false values to
1
and 0 respectively. This allows you to sum the true/false values and get
a
count of how many trues there were.

Bob Phillips has an excellent discussion on sumproduct here
http://xldynamic.com/source/xld.SUMPRODUCT.html

Thanks for that.

To be honest, I had not come across the Excel sumproduct function before. It
looks very powerful so I will enjoy reading this interesting article.

V