It may be that Excel realizes it's fully calculated when no cells
change in value by more than Maxchange. It does quit before
MaxIters. But it leaves the Calculate flag up.

And it would be nice if not refering to those cells on the interative
second pass (and thereafter) did indeed solve the problem. But as I
said before, it does not.

The UDF remains dirty because it references a cell, not because it
uses its value or state. As I said, even IsEmpty creates this
condition. This hardly constitutes true circularity!

So I think this amounts to a bug with no cure. Instead of fast array
math, I'll have to go row by row, cell by cell, and skip any cells
involved in circularity.

Charles, thanks for trying to help.

--Dean