Final answer:
The rarely used metering device suitable for constant load applications and requiring manual adjustments is an analog meter with a galvanometer.
Step-by-step explanation:
The metering device being described is likely a manual type, such as an analog meter that includes a galvanometer. Analog meters have a needle that swivels over a marked gauge to indicate measurements, and their operation relies on a device called a galvanometer. Current flow through this galvanometer causes a proportional needle deflection due to the magnetic field's effect on the current-carrying wire. In conditions where the load is constant and an operator is available to make manual adjustments, such an analog meter can be effectively utilized, although its use is rare compared to more automated systems. For example, bridge devices are employed in circuits for null measurements and can be part of a manual metering setup in specific engineering applications.