Thermometer useless? Always reads high

I'm wondering about this too. I've been running in the snow lately and it's telling me it's around 10-15 degrees centigrade out....

I think it is primarily for swimming.

A thermometer is needed for baro&altimeter on your wrist. There are some models of external bt/ant+ thermometers that you can use. 

ps Not always reads high - in the sauna it will be low :)

I can't follow you... How is temperature needed for baro and alti when they are purely based on pressure and a MSL pressure datum?

Pressure sensors are temperature compensated. But since the watch will usually be very influenced by body temperature, the readout will not make much sense. It works better in water, or when you wear the watch outside a jacket.

PV=nRT...  it's basic physics. The pressure in this sort of pressure sensing component is always going to have to be informed of the temp if that is not static.