The device in the image appears to be a Tesca Analog Portable Three-Phase Wattmeter (Type DPW3), designed for measuring electrical power in industrial or educational laboratory settings. Unit: Watts (W)
Function: Measures real/active electrical power.
Terminals/knobs: Used to select the appropriate current and voltage measuring ranges and connect the meter to the circuit.
Pointer and scale: Indicate the measured power value.
In short: It measures the electrical power used by a load and displays the value in watts.