Establishments primarily engaged in manufacturing industrial instruments and related products for measuring, displaying (indicating and/or recording), transmitting, and controlling process variables in manufacturing, energy conversion, and public service utilities. These instruments operate mechanically, pneumatically, electronically, or electrically to measure process variables, such as temperature, humidity, pressure, vacuum, combustion, flow, level, viscosity, density, acidity, alkalinity, specific gravity, gas and liquid concentration, sequence, time interval, mechanical motion, and rotation. Establishments primarily engaged in manufacturing electrical integrating meters are classified in Industry 3825; those manufacturing residential and commercial comfort controls are classified in Industry 3822; those manufacturing all liquid-in-glass and bimetal thermometers and glass hydrometers are classified in Industry 3829; those manufacturing recorder charts are classified in Industry Group 275; and those manufacturing analytical and optical instruments are classified in Industries 3826 and 3827.