I have inserted the
Application.Volatile
in my code for a custom formula as follows:

Public Function MyFormula(ARRAY1, ARRAY2, ARRAY3, sSTRING)
MyFormula = Application.Caller.Parent.Evaluate( _
"SUMPRODUCT(--(" & ARRAY1.Address & "=""" & sSTRING & """),--(" & _
ARRAY2.Address & "0)," & ARRAY3.Address & ")")
Application.Volatile
End Function

However, when I change a cell involved in any array the result is not
updated unless I make some OTHER change?

How to make a timely change so that when, for example, I change value of a
cell in ARRAY3 the result of the formula updates itself, instead of making
some other change in the workbook or pressing F9.

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Best Regards,
FARAZ A. QURESHI