Hydrometers and similar floating instruments, thermometers, pyrometers, barometers, hygrometers and psychrometers, instruments and apparatus for measuring or checking the flow, level, pressure or other variables of liquids or gases except navigational, hydrological or meteorological instruments and appliances, gas or liquid supply meters, and automatic regulating or controlling instruments and apparatus for physical or chemical analysis, for measuring or checking viscosity, porosity, expansion, surface tension or the like, or for measuring or checking quantities of heat, sound or light