I have one sheet (Sheet A) with formulae (or even formulas, if you
must) referring to numbers on a different sheet (Sheet B), which
itself has a Data Filter to help with the interim analysis of data but
needs to be set at Data Showall once finished.

What is the simplest way of getting a warning to appear on Sheet A
when the data is being masked by the use of the filter in Sheet B.

Thanks in advance, Tim