High pressure gauges measure pressure in relation to?

High pressure gauges are specifically designed to measure pressure in relation to atmospheric pressure. This means they provide readings that indicate how much greater the measured pressure is compared to the pressure exerted by the atmosphere. When a high pressure gauge shows a reading, it reflects the additional pressure above the ambient atmospheric level, which is why the correct answer is that high pressure gauges measure pressure above atmospheric pressure.

In contrast, absolute pressure gauges measure pressure in relation to a complete vacuum, providing a reading that is the total pressure exerted. Vacuum gauges measure pressures that are less than atmospheric pressure, indicating levels of vacuum. Understanding these distinctions is key in applications where accurate pressure measurement is critical, such as in various industrial and laboratory settings.