HRV Widget and HRV recording

The Log HRV function would record HRV data to an activity's FIT file if you were using a compatible external heart rate monitor during the activity. The data recorded is not displayed on Garmin Connect but some third party applications and services can display this data. (I believe Strava can if you use that service.)

The HRV Widget is related to HRV Status which was introduced with the 23.00 firmware. HRV Status uses the optical heart rate monitor on the watch to measure HRV while you sleep. At the end of the sleep period HRV Status will calculate the average HRV for the sleep period.

Super clear! Thank you!!

Show how to turn on recording  ? 

Recording of which? The OP is asking about two different measurements performing two different functions.

Tell me, and appeared in the 6th version of the watch "readiness for training" ? 

Thanks fbbbrown. I'd like to add, Runalyze.com displayes HRV data in activities without the need for a datafield. The HRV widget writes FIT files with averages over 5-minute intervals during sleep time. But the contents of these files are not documented and you will only be able to retrieve them from the watch when you do not sync to Connect.

Anyway does 71ms equal to 99 ms as explained by Garmin here: https://www.garmin.com/hu-HU/garmin-technology/running-science/physiological-measurements/hrv-status/?

I mean the 5 screenshots being in a layout of a T.

Or have I overlooked something?

Well spotted! I do not understand this discrepancy. If it were a publication in a scientific journal I'd email the author to ask. 

Even if I can spot bugs or discrepancies, there are always people around who say they are not important, these things do not have an influence on the really important things like we have a wonderful product. Like these guys in that thread https://forums.garmin.com/beta-program/fenix-6-series/f/community-discussion/305603/garmin---we-are-alpha-beta-testers---why-public-changelog-with-so-many-discrepancy-explanations-please/1477631#1477631

But if it is common and easy for me to find small bugs and obvious discrepancies, how the hell I can trust in it that much more complicated algorithms are designed and coded well? How the heck I could trust the numbers my watch is spitting out? I mean not just about the physiological measures, which are sort of black boxes for users, since the exact algorithm is are protected and hidden, but also about anything which cannot be recalculated by the users ex-post due to the lack of the basic data.

But no problem, things are in order and controlled in the best way.