ConstRenders nothing while the sheet has no cycles. Excel appends one cell (: A1); this does not
— a cycle has no first cell, and naming one reads as "the problem is A1" when B1 is just as
much in it. The cell it would name (the first member on the sheet, Worksheet. CircularReference's answer) is the readout's tooltip, and pressing it selects that cell. Read
off the sheet's Feature.Circular index, which is committed with the calculated values, so a
data change is the one signal to re-read on.
The status bar's circular-reference readout —
Circular References, shown while the selected sheet has any.