Bob Phillips explains =sumproduct() in much more detail he
http://www.xldynamic.com/source/xld.SUMPRODUCT.html

The bad news is that Bob's site is experiencing problems.

You may want to try every so often to see if it's back up.

Kevin wrote:

I have been doing a lot of reading on this function and can usually get it to
work to do the job - not overly complex.
One thing that is still not understood (and not the only thing) is what is
the difference between using * or , to separate the arrays in the argument?

Kevin

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Dave Peterson