https://apps.garmin.com/en-US/apps/17580ca9-816e-4203-a6a5-002eb543c04a
It's only for devices that allow Connect IQ to access the internal temperature history. With the Tempe, it can take a minute or more to get data, so that data is cached, so you can see the last reading while waiting (the default is after 30 minutes, it goes "stale", but can be set between 0 (never go state) to 240 minutes (4 hours). App settings also allows setting colors. The "Temperature Units" in the watch settings is used for C/F.