I came across a device called magic eye while we were being taught AC bridges. The teacher told that it was an aperture that allowed light to pass when the bridge was in unbalanced condition.
Making a search on google returned irrelvent results.
Can anyone post me a picture of a magic eye. and tell me how it works.
Can it also detect phase unbalance apart from the z1.z4=z3.z4?(hope I am not asking something silly? )
Old radios used to use a magic eye (that's what we called it) as a signal strength indicator. Several pieces of old test gear that I had used the "eye" as an indicator for peak or null. That might be what your professor meant. If that is the case I am sure that some older vacuum tube/valve manuals would adress it. I know it's in my old (1960's) ham radio handbooks.
These are the ones I remember from back in high school, round ones that would glow a in an increasing area of the circle. They were on test equipment, I think RF generators if I remember correctly.