What does the N2 gauge measure?

The N2 gauge is specifically designed to measure the rotational speed of the high-speed spool in a gas turbine engine. This measurement is crucial because the high-speed spool typically drives the components that are responsible for delivering compressed air to the combustion chamber. The N2 reading is vital for monitoring the engine's performance and ensuring it operates within safe and effective parameters. By knowing the rotation speed of the high-speed spool, engineers and operators can make informed decisions about engine efficiency and overall operation.

On the other hand, while the other options relate to different aspects of engine performance, they do not pertain to the function of the N2 gauge. For instance, measuring the speed of the low pressure turbine pertains to another gauge entirely, while efficiency of the combustion process and thrust production are evaluated through different performance metrics. Understanding these distinctions helps ensure accurate assessments of engine performance and safety.