Does anyone understand the physiological metrics

I have same question reg HRV in FR245

1. So, when you say third party tools do you have an example. I hate to be a pain, I'd just really like to see the data but can't find a way. 

I'm sorry but I don't remember. I think there was a discussion about it on the garmin forum some time ago.

For examble, with the device app Meditate https://apps.garmin.com/de-DE/apps/1cc98099-c08b-4fc7-91e6-0f3615a3ab2c
u can see and store HRV data in Garmin Connect Web and Garmin Connect Mobile.
There is bound to be more apps.
Just try it.