> I'm more curious about how the physicist worked out a spectral plot by hand before sampling and FFTs were invented and oscilloscopes were barely a thing. Bef

> I'm more curious about how the physicist worked out a spectral plot by hand before sampling and FFTs were invented and oscilloscopes were barely a thing. Before there were digital FFTs, there were analog equivalents. A prism basically does an FFT on light. I don't know, but I'd bet there were many analog based frequency analysis tools available before digital frequency analysis.