Is there a reason we don't have advanced metrics on watch faces?

Yes, it's about the battry life. Watchfaces are very limited in what they can do. The majority of the time, a watchface only updates every minute (but a wrist gesture will allow it to update every second for about 10 seconds, allowing seconds to be display)

There is no access to sensors, GPS or comm from a watchface. Some watchfaces will use data from your last activity (as that is preserved in the FW for a while) and use things like that last lat/lon for sunrise/sunset calculation, and display things like the last known elevation.

What type of primary stuff are you looking for?

There is no access to sensors, GPS or comm from a watchface. Some watchfaces will use data from your last activity (as that is preserved in the FW for a while) and use things like that last lat/lon for sunrise/sunset calculation, and display things like the last known elevation.

What type of primary stuff are you looking for?

I'm happy for just a snapshot, an average over an hour or just less frequent measurements. The main ones I'm interested in are temperature (Tempe sensor) and barometric pressure. HR would also be nice but I understand the implications of this on battery power. An hourly average would be better than nothing.

As I said, no access to the sensors in a watchface, so all you can get in info on your last activity. And Temperature (from a Tempe) isn't availbe there.

However, there is a watch-app that looks like a watchface, and uses the Tempe (I know the guy that wrote it! :) )

https://apps.garmin.com/en-US/apps/54e90766-dc58-4f42-b898-261a090949c5

It's only for the fr23x/630 and vivo active right now. What watch do you have? It can't work on the 920, as the Tempe isn't a standard sensor on it, and I don't want to do the low level Ant+ stuff myself.