Set db = CurrentDb
Set rs = db.OpenRecordset(prProdTblName)
'PrevDept , PrevOpNo, PrevPartNo
rs.MoveFirst
rs.Edit
rs![Op No] = 10
rs.Update
Do Until rs.EOF
    With rs
        PrevOpNo = ![Op No]
        PrevDept = ![Department Code]
        PrevPartNo = ![Part No]
        .MoveNext
        .Edit
        If (![Department Code] = "SMD" And PrevDept <> "SMD") Then
            ![Op No] = 500
        ElseIf (![Department Code] <> "SMD" And PrevDept = "SMD" And ![Part No] = PrevPartNo) Then
            ![Op No] = 1000
        ElseIf (rs![Part No] <> PrevPartNo) Then
            ![Op No] = 10
        Else
            ![Op No] = PrevOpNo + 10
        End If
        .Update
    End With
Loop
rs.Close
Set rs = Nothing