'firstdate, lastdate ermitteln
            Dim firstdate = (From drv In ArchivDB.AblesedatenStrom Where _
              drv.RowState <> DataRowState.Deleted Select drv.Ablesedatum).Min
            Dim lastdate = (From drv In ArchivDB.AblesedatenStrom Where _
            drv.RowState <> DataRowState.Deleted Select drv.Ablesedatum).Max