I really have no clue what this thing is used for.
It is some kind of balance bridge. There are resistors between the banana conectors at the back. It is symmetrical. The knob on the front is connected a potmeter to balance the bridge. The meter is a null meter. This potmeter is huge. It is the size of the scale you see on the front. The back potentiometer knob adjusts the sensitivity of the meter.