9 BOATING EQUIPMENT-NAMELY, SCIENTIFIC, NAUTICAL AND ELECTRICAL APPARATUS AND INSTRUMENTS, MEASURING, SIGNALLING AND CHECKING APPARATUS AND INSTRUMENTS-NAMELY, CATHODIC PROTECTIVE DEVICES AND SYSTEMS-NAMELY, CURRENT AND POTENTIAL METERS, POWER SUPPLIES, REFERENCE ELECTRODES, PLATINUM ANODES, THROUGH-HULL FITTINGS, CASES AND WIRING FOR NAUTICAL CATHODIC PROTECTIVE DEVICES AND SYSTEMS