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SUMX() – the great iterator

Have you ever written an array formula in Excel?  (Don’t worry, most people haven’t).  Have you ever written a FOR loop in a programming language?  (Again, don’t worry, there’s another question coming).  Have you every repeated something over and over again, slowly building up to a final result?

That’s what SUMX() does.  It loops through a list, performs a calc at each step, and then adds up the results of each step.  That’s a pretty simple explanation, but it produces some results in pivots that are nothing short of spectacular.

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