I want to create a column in the data field that will show me the difference between the two columns. I thought I had the correct code but when I run the code, the error message I get is an incorrect method for the field. Not sure where I went wrong...ideas?

(This is my current code)

Sub CreateAPivotTable()

Dim shtSource As Worksheet
Dim rngSource As Range
Dim rngDest As Range
Dim pvt As PivotTable

On Error GoTo ErrHandler

'this prevents the screen from updating while the macro is running and
'will make the code run faster
Application.ScreenUpdating = False


Set shtSource = ActiveSheet

If shtSource.Name <> "Summary" Then

'Rather than have the pivot table use all rows in column A-N
'just use what has actually been used.
Set rngSource = shtSource.Range("A1").CurrentRegion

'This is where the pivot table will be placed
Set rngDest = shtSource.Range("E1")

'This creates a pivot table. So rather than having to refer to PivotTables("PivotTable14") like before you can just refer to pvt
Set pvt = ActiveWorkbook.PivotCaches.Create(SourceType:=xlDatabase, SourceData:=rngSource, _
Version:=xlPivotTableVersion12).CreatePivotTable(TableDestination:=rngDest, _
DefaultVersion:=xlPivotTableVersion12)

pvt.AddDataField pvt.PivotFields("Serial Rcvd"), "Count of Serial Rcvd", xlCount
pvt.AddDataField pvt.PivotFields("Serial Shipped"), "Count of Serial Shipped", xlCount
pvt.PivotFields("Count of Serial Rcvd").Caption = " Serial Rcvd"
pvt.PivotFields("Count of Serial Shipped").Caption = " Serial Shipped"

With pvt.PivotFields("Item")
.Orientation = xlRowField
.Position = 1
End With

With pvt
.CalculatedFields.Add Name:="Devices Owed", Formula:="Serial Rcvd-Serial Shipped"
.PivotFields("Devices Owed").Orientation = xlDataField
.NumberFormat = "0,000#"

End With

'Formatting
pvt.TableStyle2 = "PivotStyleDark7"
With shtSource.Cells.Font
.Name = "Calibri"
.Size = 8
.Strikethrough = False
.Superscript = False
.Subscript = False
.OutlineFont = False
.Shadow = False
.Underline = xlUnderlineStyleNone
.ThemeColor = xlThemeColorLight1
.TintAndShade = 0
.ThemeFont = xlThemeFontMinor
End With

ActiveWorkbook.ShowPivotTableFieldList = False
Else
MsgBox ("Please remove existing sheet with the name of Summary")

End If

Application.ScreenUpdating = True

Exit Sub

'Simple error handler in case something goes wrong
ErrHandler:
Application.ScreenUpdating = True
MsgBox "An error occurred: " & Err.Description, vbExclamation, "Error"


End Sub