The device appears to be a Meco-G Portable Electrodynamometer-Type Power Factor Meter (Cos φ) housed in a wooden carrying case. Function:
It is used to measure electrical power, reactive power (VAR), and power factor in three-phase AC circuits, for both balanced and unbalanced loads.
Brief statement:
A 3-phase electrodynamometer meter is used to measure active power (W), reactive power (VAR), and power factor (cos φ) in AC electrical systems.