Termperature

The built in temperature sensor is for the barometric altimeter. As stated, the watch can be removed and used to find ambient temperature, but you're better off using an external tempe sensor for that.

The internal sensor is used in connection to the baro altimeter, and it will show the watch temp, which on your arm is impacted by body heat, or by wearing long sleeves or a jacket. You can get a Tempe Sensor (it looks like a Garmin Foot Pod), and have that give you a better ambient temperature. Here's a widget where you can see both. There's also watchfaces that will get weather data from the internet.

The temperature is needed for the accurate barometer readings, I guess. But it's useless for the person wearing it. I think Garmin added a widget for it in the spirit of "what the heck, let's add it" but I really wish they'd have exercised some restraint and left it off. I'm a junior grade programmer and I've learned that a half-assed feature pisses people off more than a missing feature.

Remove the widget. Problem solved. As already stated, the widget and sensor can be used for ambient temperature readings also. Just because you feel it's a half-assed feature that pisses you off doesn't mean others do too.

I have to side with those who feel it's not well thought through from a user experience point of view. I upgraded to the 645 and now get temperature data on Garmin Connect from every run which always shows the temp declining from what it was at the start...nowhere does it say what I'm supposed to gain from this data (like the other features do). Sorry to reply 3 years late!

nowhere does it say what I'm supposed to gain from this data

This is the same argument you hear about with heart rate with the oHRM vs a strap. If you want more precise data, get an external tempe sensor.

temperature data on Garmin Connect from every run which always shows the temp declining from what it was at the start.

For my activities the temperature reading reflects changes in shade, sun shining on watch arm or not, breeze and environment in general. I accept the information I have read indicating that the specific temperature reading will be wrong due to the influence of my body temperature, however I have found that the relative value increases and decreases in ways that make sense during an activity - just like the barometer, in fact.

I have found reduced pace at times corresponding exactly to increases in temperature. I gain from this data, just as I gain from the elevation trace telling me when I reached the beach even though it is not labelled '1m above sea level'.

I prefer having more and understandably imperfect data to the alternative; my frustrations with the watch are all down to -not- having access to raw data like heart rate / HRV for sleep and satellite quality for pace. Please don't ask to dumb down my watch any more than it already is.

5 or 10 degs higher. lucky you my 645 music was reading 299 at the moment!!! anyone have any idea how to fix this?? I have reset the watch and now its reading 569!!!

I bought an external sensor (Tempe) and it works great. I get good readings during activities.
Daily use not so easy as most watch faces and widgets can only use internal temperature sensor.

On some watches, when you have a tempe paired, the native temperature widget looks for that and doesn't show the internal temperature.

So I wrote Temps It shows both, and caches the tempe data for a user configurable time, so you can see both (the cache is because it can take a minute to get data from the tempe)

While not a watchface, I also have an app that looks like a watchface that uses the tempe Time and Tempe.

I find the tempe a bit easier to use with the addition of an S-Biner #3 clip, so it can be attached where needed (~$2US)

There's a picture in the Time and Tempe app in the store.