vba excel - Pivot Tablle Calculated Field - vba

Question

I have developed a Pivot Table and need to add a calculated field. Rather than using the 'named' (row) fields, I would like to use the 'reference' field in my calculation. The formula works fine using the 'named' field. but not when using a 'reference'. Below is part of the code and where is goes wrong. Appreciate your guidance and help.
'/-------------
'/ Insert Data Field
'/-------------
With pTable
With .PivotFields(wksDSheet.Cells(1, 5).Value)
.Orientation = xlDataField
.Position = 1
.Function = xlSum
'NumberFormat = "#,##0.00"
.Caption = "Actual Spent"
End With
s1 = pTable.PivotFields(wksDSheet.Cells(1, 5).Value)
With .PivotFields(wksDSheet.Cells(1, 6).Value)
.Orientation = xlDataField
.Position = 2
.Function = xlSum
'.NumberFormat = "#,##0.00"
.Caption = "YmBudget To date"
End With
With .PivotFields(wksDSheet.Cells(1, 7).Value)
.Orientation = xlDataField
.Position = 3
.Function = xlSum
'.NumberFormat = "#,##0.00"
.Caption = "YrBudget To Year"
s2 = pTable.PivotFields(wksDSheet.Cells(1, 7).Value)
End With
End With
'/-------------------
'/ Insert Calculated Fields
'/-------------------
'/ The Name and Formula
''' This works''''>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
' pTable.CalculatedFields.Add Name:="Available", _
Formula:="=YrBudget - Actual"
''' This does NOT work ''''>>>>>>>>>>>>>>>>>>>>>>>>
pTable.CalculatedFields.Add Name:="Available", _
Formula:="=s2 - s1"
With pTable.PivotFields("Available")
.Orientation = xlDataField
.Function = xlSum
.Position = 4
'.NumberFormat = "0.00"
.Caption = "Net Available"
End With