Final answer:
A system vacuum gauge should be attached to a part of the system where it can accurately measure the pressure, like the intake manifold for engine diagnostics or to a vacuum chamber in physics experiments.
Step-by-step explanation:
The system vacuum gauge should be connected to a point in the system where it can measure the pressure accurately. If we talk about a vacuum chamber used in physics experiments, the gauge would be connected to the chamber in order to read the pressure inside, which is less than atmospheric pressure. For measurements during an engine's operation, such as a car's internal combustion engine, the vacuum gauge should be connected to the intake manifold to monitor the engine vacuum, which assists in diagnosing engine performance issues.
Gauges that measure pressure relative to atmospheric pressure are known as gauge pressure instruments. When working on physical systems such as engines or scientific experiments, where continuous pressure reading is required, a gauge that can provide continuous measurements during the operation phase, like during the expansion phase in an engine, should be used.