Can pressures below atmospheric pressure be measured in inches of mercury column?

When measuring pressures below atmospheric pressure, it is indeed possible to express these values in terms of inches of mercury (inHg) column. This measurement is commonly used in the field of HVAC and other engineering disciplines to represent vacuum pressure. A vacuum is defined as a pressure that is lower than atmospheric pressure, and using inches of mercury as a unit allows for a clear understanding of how much lower the pressure is compared to the ambient atmospheric pressure.

In practical applications, vacuum gauges often utilize inches of mercury to indicate the degree of vacuum achieved. For example, a reading of 28 inches of mercury would suggest a pressure that is significantly below standard atmospheric pressure, which is useful information when evaluating the performance of air conditioning and refrigeration systems.

The other options suggest limitations or incorrect notions about measuring such pressures. Some may imply that specialized instruments are required or that no measurement in inches of mercury can be made at all, which is not the case. Thus, the ability to measure pressures below atmospheric in inches of mercury is not only possible but also a standard practice in various scientific and practical applications.