Off Topic Banter

[L67GS]

a resistor, a capacitor, and another resistor, all in series.

Trial and error noise filter?

[mctom]

Probably trial and error AC coupling, but indeed it looks like something they copied over without giving it much thought.

Huh, by the way I learned what this instrument is even for. I knew it was some sort of medical device, but I wasn't aware it was specifically for diagnosis of .. sleep apnea.
Isn't it ironic? Perhaps I'll just have one unit as a payment

[mad_ady]

You can get one, but you won't be sleeping well, thinking what those components are supposed to do...

[mctom]

Last night I couldn't sleep thinking how uncomfortable this must be for belly sleepers. It's strapped right on a patient's chest, because it does ECG as well.

[L67GS]

That could potentially help to smooth out a wave, like help pwm look more like a sine.

[mctom]

That could potentially help to smooth out a wave, like help pwm look more like a sine.

Perhaps my circuit description wasn't clear , but that's definitely a high pass filter. AKA "AC Couple" because it doesn't pass DC at all.