[cess11]

I'd sneak in 'Toggle C/F' somewhere and hook it to the same function you use on the numbers.

Fahrenheit goes negative at a measly -18C. Where I live -20 to -30C is not uncommon. Whether it's 17.5 or 18C typically does not matter, continual changes in wind and other factors will for pretty much all practical purposes quench that difference.

[Leftium]

Fair enough. I added a toggle button and removed decimal °C.

Weather uncertainty may make that extra precision less useful.