JoeU2004 wrote:
"... or by including it in the computation, e.g. MarkP(...)+Z1 or
MarkP(...)&Z1 depending on the type of the value returned by the function.


including non parameter in computation does not call a function


Function aaaa()

aaaa = Range("a1").Value + 1

End Function


changing A1 value does not change value of a cell where function is used.

in general udf function result should depend only on parameters passed
to a function.