What do low side (compound) gauges measure?

Low side (compound) gauges are designed to measure both pressures above and below atmospheric levels. This characteristic is particularly useful in systems that involve refrigerants or fluids that can exist in both a gas and liquid state, as well as in vacuum conditions.

When measuring above atmospheric pressure, the gauge displays pressures in a positive range, indicating how much pressure exists in a system compared to the ambient atmosphere. Conversely, when the system experiences a vacuum (pressure below atmospheric levels), the gauge is capable of indicating how deep that vacuum is relative to atmospheric pressure. This dual functionality allows for comprehensive monitoring and diagnostics of systems, such as refrigeration and air conditioning, where pressure variations are crucial in operation and maintenance.

In contrast, gauges that measure only high pressure would be unable to provide readings for vacuum states; those that measure above atmospheric pressure only would lack the capability to indicate negative (vacuum) pressures; and gauges solely designed for vacuum levels would not cover the full spectrum of pressures that may be encountered in these applications. Thus, the ability of low side (compound) gauges to encompass both above and below atmospheric pressure makes them versatile tools for various measurement needs.