[Findm-Keepm]

It's used to display the phase relationship between two sinusoidal waveforms, usually the outputs of synchros or resolvers, as someone mentioned.

The reference input is the signal measured from - that is, the signal input will be 0-359 degrees leading or lagging the reference. We used them in the Navy quite extensively - they saw heavy use in autopilot/auto stabilization (avionics) equipment testing. North Atlantic was a manufacturer of one phasemeter we used, and they also make phase angle voltmeters as well.

A Phase meter has to work with varying voltages and frequencies, like 60Hz, 400Hz (airvborne), 115VAC, and 26VAC systems, the latter being common in aviation.

The one you have sounds like one that we had installed in our shipboard jet engine test cells, used to remotely measure the angle (deflection) of inlet actuators. You'd compare the other performance factors to the phasemeter reading to determine the optimum settings for an jet engine "run" on the cell
Useful item to those who need it - I'd personally save it from the scrap pile, as the new LCD based meters lack the "cool" factor of nixies.

Cheers,