Subtract cell formula from existing cell formula

[transferxxx]

Does anybody has a macro which would deduct the cell formula of a
selection of cells from original formula.
eg if cell A1= sum(b1:f1)
the macro would leave formula in A1 as : sum(b1:f1) - sum(b1:f1)

so that formula result of A1 would be zero

 

[Gary''s Student]

Sub whybother()
Dim r As Range
Dim s As String, s2 As String
For Each r In Selection
s = r.Formula
s2 = WorksheetFunction.Substitute(s, "=", "")
r.Formula = s & "-" & "(" & s2 & ")"
Next
End Sub

 

[transferxxx]

thxs - working great !!

Sub whybother()
Dim r As Range
Dim s As String, s2 As String
For Each r In Selection
s = r.Formula
s2 = WorksheetFunction.Substitute(s, "=", "")
r.Formula = s & "-" & "(" & s2 & ")"
Next
End Sub