Rhythm of War has a bit more focus on technical intricacies of the magic system. Navani is one of the primary viewpoint characters in it

Fahrenheit’s 0 is the freezing point of water - salt water that is. Not that I think it’s better, just that there was some thought put into it.

In the context of Iroh’s character it makes complete sense though. He had a… “grand” life as a general in the first nation, but realised it was not what he wanted when his son died in the army. At least, if I remember correctly.