RSSI Units, Logs vs. Z-wave details

I'm getting inconsistent results in my Z-wave mesh. So, I want to see which devices have weak signals.

The z-wave details reports RSSI in db--but relative to what? Every result in positive, so, the bigger the number the bigger the signal, but the report in "db" makes me suspicious something is off...

The logs report dbM, which makes sense. It's really an absolute measurement, since the db's are relative to 1 Mw.

Everything is negative in the logs, the less negative, the stronger the signal.