Function to Check if Cell is hidden

[ThomasD]

I have set up a filter, and the rows filtered out shall contain a
different calculation than the visible rows.

So the Problem is a function like ishidden() to get the information
that a cell or row is filtered out.
e.g. =if( ishidden( A4 ); A3; A3+1 )

Function isHidden( oCell as Object ??? )
###need this desperately, the argument may be optional
or can be left out (=current cell) when easier###
End Function

I appreciate your soon help THANKS. Other solutions possible?

Thomas