A tachometer is useful for troubleshooting which of the following issues?

A tachometer is a device specifically designed to measure the rotational speed of a shaft or disk in engines and other machinery. When troubleshooting, being able to monitor the speed of moving parts is critical because it can help identify if equipment is operating within its designed parameters.

While pressure and flow are important parameters in many systems, a tachometer does not provide direct information about these factors. For instance, flow can be influenced by many variables not directly related to the rotational speed, and pressure readings are typically taken using different instruments like pressure gauges or transducers.

However, speed can impact flow in certain systems, particularly in pumps or engines where the speed of rotation correlates to the flow rate. Therefore, a tachometer is useful in indirectly assessing flow issues by ensuring that the machinery is operating at the required speed to maintain optimal flow. This connection makes it relevant to both speed and flow, hence supporting the answer that encompasses both factors as part of troubleshooting measurements.

In summary, the correct answer takes into account the functionality of the tachometer in measuring rotational speed and its indirect relationship with flow, making it a versatile tool in troubleshooting scenarios.