I looked it up. It is something to do with how the sensors work. Under certain conditions they will report negative. Either way, the point was, I don’t see this machine being able to do much if it needs around 20%…

I think technically what we call humidity is actually relative humidity, so it can go below zero. Ture humidity can’t of course.

Doesn’t SoCal sometimes have negative humidity? 20% seems pretty high to say it works in the desert.