The ground isolated serial connector (GISC) is used to break ground loops between your PC and the AquaController. In some installations a ground loop is formed when a serial connection is made and can cause erroneous pH and ORP readings. This ground loop can be broken by installing a GISC in the series with the serial cable from the AquaController. The GISC measures 2.5" x 2.25" x .65" and has one male DB9 connector and one female DB9 connector.