What kind of measurements do pressures such as 20.4" hg and 20.0" hg represent?

The measurements of 20.4" hg and 20.0" hg represent pressure readings. These figures indicate the level of atmospheric pressure or the pressure exerted by a gas above a liquid in a system. In refrigeration and many industrial applications, pressure plays a critical role in determining how gases and liquids behave. Understanding these pressure measurements is essential for determining the efficiency of refrigeration cycles, the operation of compressors, and the overall management of refrigerant fluids in industrial processes.

While vapor density relates to the mass of vapor in a given volume and influences how gases behave, it is not directly what these specific measurements represent. Evaporator temperatures are typically derived from pressure readings but are not themselves what the readings illustrate. Liquid mass concerns the actual weight of a liquid volume, which is distinct from the pressure exerted by it. Therefore, the context and application of these measurements firmly categorizes them as pressure readings.