Why does Sunlu S4 say 21% when meter says 10%?

[krellboy]

Filament Drying preliminary results

I’ve speculated that this might be the case for some dryers where the sensor in mounted on a PCB that straddles the exterior and interior, especially if the board is insulated with a shroud on the inside. The sensors are designed to have the body at the same temperature as the measured air and not be mounted on a relatively cool PCB. There are at least 3 or 4 people on here who are interested and personally I’m into the equations side, so feel free to go full nerd.

TLDR, not designed very well.