1) That post is old. 2017. Since then (sometime in 2018) as I understand it, Espressif started "calibrating" the ESP32, and putting in the calibration value in the Block 0 of efuse. See: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/adc.html The "default" 1100...

I guess, lets start over. I've run the comparison of the ~1.66v output on three different esp32 boards. The output is all quite close. 1.48/1.51/1.47. Are all ESP boards this bad? I'd be more-or-less fine if they were a few hundredth's of a volt off. But 0.15v off? That's pretty bad, IMO. I'm using ...

I think you need the vref from efuse, about 1.1V. You said it read 1.46 when you measured 1.6, that would explain the difference. Explain that to me, because it doesn't make any sense. 1) I thought efuse changed the voltage calibration, so that the output from the ADC's would be "corrected" when qu...

I'm just using the raw non-voltage-divided 18650, but keeping the output range <3.3v. 18650 -- POT -- ESP (If it was a fixed amount "off" in the whole range, I'd be happy.) I also saw a post about measuring the ESP's own 3.3v output, with a voltage divider, and using it as an "adjust" reference. Wit...

Honestly the seller you purchased them from should give you that data.
There's a ton of different boards, and us trying to find the "right" one seems pretty fruitless.
Ask the vendor you purchased them from!

So, I've read a ton of forum posts here and elsewhere - I get the non-linearity of the ADC, at below 0.5v and above 2.5v. I know about the attenuation, etc. But the voltages I'm reading from the ADCs are just wrong - and don't fit any of the details I've read about. I assume I *must* be doing someth...