Edge 840 - Max Heart rate bug

This is confusing, but the Edge is actually doing two different things.  The max value in the summary is the actual max value you hit.

The max value in the highlight is a computed max value produced by the Firstbeat libraries from a submaximal effort using the HRV data.

If you switch off the  auto-detect max HR is will stop using the Firstbeat libraries to compute a max value.

Thank you - yes it is confusing! 

>>>a computed max value produced by the Firstbeat<<<

I never paid attention but that's interesting.  It's a theoretical absolute max HR extrapolated from the workout.  I'll have to look at it after my next ride. Is there a specific HRM that needs to be used to get the HRV, and does it need HRV tracking off the bike?  I just tried to find info on this but was unsuccessful.  Where should I look?

for me it is working a bit weird (especially indoor since 3months) , it is continously decreasing my computed maxHR, it is only 180bpm now and i know i can reach more, just my position is very static on the bike, like a statue, no upper body movement. and probably my lowHR drift can fool it, i dont sweat for 30-40mins for sure (too good cooling .. ) and probably this is why my HR is low even with longer 3xx watts also (under threshold). 

and my other issue is the auto-ftp calculation, i rode 120mins at 300avgwatts on Neo, (305NP), ERG mode, and the 840 gives me 294w for estimated FTP  , completely idiot algorhythm...  

i use Polar H10 sensor via BT for HRV tracking (it is for a 3rd party app, via BT the errors are 0 or close to it), but any Garmin hr sensor is good enough for the inbuilt HRV analysis.

Welp.  Here's a recent article from CTS about these proprietary "black box" algorithms being more marketing than science.  I figure if  I don't know how it's calculated or validated, I don't know how to use it or if it can be trusted. 

https://trainright.com/new-study-reveals-holes-in-wearable-device-scores/