Order Analysis Using Zoom FFT since 1979 ~ 1981

[Kiriakos GR]

I have one interesting find to share about Order Analysis Using Zoom FFT.
Internet search while this is not (never was) reliable, at the delivery of the information that you do seek, careful inspection of random finds, it might include a treasure. 

I did find an fact that Order Analysis Using Zoom FFT = digitizing of energy for analysis, this started at the year 1979 and later (In the USA).
Back then they did not have electrical energy pollution as we know it today, this be caused due of all our electrical appliances, or due the mix of many renewal energy sources with the grid.

At 1980 electrician engineers working at manufacturing of measuring and power analysis tools, was had in focus harmonic content this caused due the rotation of very large motors.
The long story in sort, electric motor rpm were explored, because slower rpm was the reason of causing higher amount of harmonic content. 

Photograph (picture) bellow, of one of the first FFT analyzers that humans succeed to make.