Recommended
(1/4) Intro/History: Introducing a 100-year-old mechanical computer
Why people recommend it
A demonstration of a mechanical harmonic analyser that performs Fourier analysis with no electronics, shared because the machine itself is worth seeing.
Watch for: Curiosity viewing rather than a practical tool
In their words
This can be done on the - literally - bare metal level using the Harmonic Analyzer:
AndreKR on electronics.stackexchange.com, Mar 2019. CC BY-SA.