Scientific, nautical, surveying, photographic, cinematographic, optical, weighing, measuring, signalling, checking (supervision), life-saving and teaching apparatus and instruments; apparatus and instruments for conducting, switching, transforming, accumulating, regulating or controlling electricity; detectors; electrical detectors for locating hidden objects; metal detectors; metal detectors for use in hobby metal detecting, metal detectors for use in security metal detecting, metal detectors for use in underground utility metal detecting, water level detectors, leak detectors for locating liquid leaks, and receivers and transmitters of electronic signals used to locate pipeline paths and blockages