Have you seen this page
http://www.xldynamic.com/source/xld.SUMPRODUCT.html.

No, I hadn't. Thanks for the link. I have doped out most of what is there on
my own. I tend to learn (retain for a longer time) things if I fight my way
through them using trial and error until what is going on finally reveals
itself. This is the method I used to learn the various computer languages I
met up with across the years (I am a totally self-taught programmer with no
formal classroom time in any of the languages I know). Not necessarily a
recommended learning method for others to follow, but it has served me well
across the years. I did find the examples helpful though... they tend to
give me situations that I might not come across (or think of) in the trial
and error approach I use. The key, for me, is to internalize the underlying
core concepts of whatever I am learning and, from them, build whatever
solutions the problem at hand requires. Thank you again for the link.

Rick