Flow gauges for measuring the flow of oxygen; Flow measuring apparatus, namely, gauges; Flow meters; Fluid flow meters; Gas flow meters; Meters for measuring gaseous flow; Fluid metering apparatus in the nature of meters; Fluid meters; Gas metering devices in the nature of meters; Gas meters; Flow pressure meters; Gas detecting apparatus in the nature of meters; Gas detecting instruments in the nature of meters; Gas masks; Gas pressure indicators; Gas sensing devices in the nature of meters; Gas sensors for measuring gaseous flow; Indicators for the optical monitoring of pressure of gases; Fluid level sensors; Level gauges; Gauges for measuring the air content of storage tanks; Gauges for monitoring the air content of storage tanks; Pressure controllers in the nature of gauges; Pressure gauges; Pressure indicators; Pressure measurement apparatus in the nature of gauges; Aerometers; Air analysis apparatus; Apparatus for the analysis of air; Apparatus for measuring pressure; Instruments for measuring pressure; Pressure measuring apparatus; Measuring apparatus for air pressure; Measuring instruments for air pressure; Measuring sensors for air pressure; Concentration meters; Calibration instruments in the nature of sensors; Gas flow detectors; Signalling apparatus and instruments in the nature of gauges for indicating gas flow pressure; Filters for respiratory masks; Oxygen masks, other than for medical use; Protective masks, other than for medical use; Compressed air emergency respirators, other than for medical use; Laboratory equipment in the nature of aspirators; Breathing apparatus, except for artificial respiration in the nature of oxygen breathing units; Oxygen sensors for environmental use, other than for medical use