@Circuitfantasist Well, when I was 10, I heard about scientists in 1600's doing experiments with frogs, using electricity as a signal to move the frog's legs. Fast forward to 2010's I was curious to know what is ECG. So I went to a hospital to do ECG, and later I had the opportunity to play with handheld and desktop ECG machines, so I spent some two hobbyist weeks learning how to do ECG.

At that time, I google for ECG toys, and found a startup project called Bulgaria Olimex was selling cheapy EKG board, which I think it the first of its kind. I bought two Olimex ECG board and learned about how they design circuits using virtual ground using human right leg, and how to use low pass filters to eliminate high frequency noises, ... , tunneldiode.blogspot.com/2020/12/olimex-ecg-modules-part-2.html***

TL Fong, I have no experience in ECG circuits but I know they are very sophisticated. But I would be happy to figure out the tricks used in them. Here is how I have explained, with a lot of imagination and intuition, the so-called right leg driven circuit...

As you can see, the idea was rated with 0 reputations while the elite received a dozen of them for a dry and formal explanation... This is a good illustration of Einstein's thought that I used as a motto at the top of my Wikipedia user page.