Which of the following is classified as a type of indicator?

A gauge is classified as a type of indicator because it is a device that visually represents the measurement of a specific variable, such as pressure, temperature, or flow rate. Gauges provide immediate, real-time data to operators, allowing them to monitor the operation of a system effectively. This visual representation helps in assessing the performance of equipment and processes, making it a crucial tool in instrumentation.

Transducers, on the other hand, are devices that convert one form of energy into another and may not directly provide a readout; they typically work as part of a larger system. Recorders provide a paper trail or digital log of measurements over time but do not serve as immediate indicators. Controllers are devices that take action based on measurements and set points but are not themselves indicators of a process variable.