"T. Valko" wrote...
....
About the volatile INDIRECT...

"T. Valko" wrote...
It appears that a formula with a volatile function used
as a validation rule doesn't "act" volatile. In a test file
I entered the validation rule using INDIRECT. Closed
the file, opened the file, didn't do anything at all, then
closed the file without Excel asking if I wanted to save
changes ( a telltale sign that a volatile function is in use)

Any thoughts on that?

Validation rules only apply when you enter something into cells with
validation rules. If you're not entering anything, e.g., when saving
files, then the validation rule wouldn't be evaluated. Key point:
validation rules are OUTSIDE the calculation dependency tree.

Validation permits initial entry, which in turn triggers minimal
recalc, which also recalcs all formulas that call volatile functions,
then evaluates the validation rule and takes appropriate action. In
that context, custom validation formulas are ALWAYS volatile no matter
what functions they call since validation rules are ALWAYS evaluated
upon entry.

Also, FWIW, if you select multiple cells, if the active cell doesn't
contain a validation rule but other selectedd cells do contain
validation rules, you could type anything you want in the active cell
and press [Ctrl]+[Enter], and Excel will happily enter the active
cell's value into all the cells without triggering validation in the
other selected cells. IOW, validation rules are only evaluated for the
active cell at the time of entry. And, as commonly known, validation
isn't triggered by pasting into cells with validation rules. If the
OP's users could be pasting values in from other programs (e.g.,
copying from PDF files), no validation rule will help. Only event
handlers and validation formulas in other cells provide relatively
robust validation. Excel's own Data Validation feature is an
unreliable toy, as industrial strength (NOT!) as internal passwords.