Liquid-in-glass thermometers, digital pyrometers for high-temperature industrial processes, aneroid and mercury barometers, and humidity-measuring hygrometers and psychrometers are all captured within this heading, which also encompasses combination instruments integrating two or more of these measurement functions. The diversity of end-use sectors — from HVAC and meteorology to food processing and laboratory science — means that the specific measurement principle and construction (e.g., bimetallic vs. resistance thermometer, floating vs. electronic hydrometer) are the primary classification anchors. Combination instruments are classified here when the combined functions are all drawn from the listed instrument types.

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