If an HVACR technician reads 25 in Hg, which type of gauge are they using?

In this scenario, a reading of 25 inches of mercury (in Hg) indicates that the technician is measuring a vacuum level. This specific measurement correlates with a gauge that can measure both positive and negative pressures, which is a characteristic feature of a compound gauge. A compound gauge can display pressures above and below atmospheric pressure, often indicated in psi (pounds per square inch) for positive pressure and in Hg when measuring vacuum.

While a pressure gauge typically measures only positive pressures above atmospheric levels and a vacuum gauge measures only vacuum levels, a compound gauge does both. The mention of inches of mercury specifically points to a measurement characteristic of vacuum readings, confirming that the equipment being referenced must have the capability for such measurements.

The manifold gauge, which is commonly used in HVAC applications, is primarily associated with refrigerant pressure measurements but can also contain compound gauges within its configuration. However, the explicit reading of 25 in Hg directly implies that we are focused on the characteristic of a compound gauge due to its dual measuring capability.