In general, what would be the best way to show an error message from a vba
function ?

I've tried a MsgBox call, but this is anoying when the function editor
(shown after clicking the = button) is used. The function editor tries to
evaluate the function before all parameters are entered completely. This
causes an error in my vba function which then interrupts the parameter
selection with the message box.

Is there some way to determine is the function editor (is it called this way
?) is visible ? so I can surpress the error message in that case ?

TIA for any help !

Jaap Versteegh