McIntosh MI-3 Maximum Performance Indicator?

A friend of mine gave me a McIntosh MI-3 Maximum Performance Indicator. It's not working. What is this thing? What does it do? Is it worth repairing? I searched the archives, nothing comes up. Thanks all, Jeff
Call Audio Classics in NY, (607) 766-3501. Or E-mail Mike or Steve at under their names. They will be great help and may be able to guess what is wrong with it and repair it for you. Check their web site out. Off cource they will not be in till Tuesday Sept 3rd. They might be able even to get you a manual for it or give you a idea what it is used for. I only think it is some kind of test equipment used to check Mac for certain things like multipath, etc. It is the older model to the MPI4.
MI-3 is a oscilloscope, used to check your FM stereo
performance. It has a multipath indicator to maximum the performance by calibrating & balancing with the scope,like meter reading. Your pattern will show you the stereo separation, left & right balance and system phase. there is a vertical and horizontal position that comes up onthe scope. In the early 70's it was worth having. In the mid 70's they came out with MIP-4 scope which was a much better buy. I have had them both.