Vacuum gauges are calibrated in inches of what substance?

Vacuum gauges are commonly calibrated in inches of mercury, which is especially relevant in the context of measuring vacuum pressure. The use of mercury as the standard is due to its high density, which allows for more accurate and sensitive measurements of vacuum levels. When vacuum pressure is expressed in inches of mercury, it reflects how many inches high the mercury column is raised by the vacuum pressure being measured. This standard is widely accepted in various applications, including industrial and scientific contexts, making it essential for technicians and engineers to understand this calibration for effective and accurate pressure measurements.

In comparison, while other substances such as water or oil can also be used for pressure measurement in specific circumstances, they do not provide the same level of sensitivity and accuracy as mercury. Additionally, air is not a suitable reference substance for this purpose, as it is a gas rather than a liquid and does not have a measurable column height like liquid substances.