965 and External HRM

Thanks for the quick reply. The manual for the 965 states:

"Enables or disables the wrist heart rate monitor. The default value is Auto, which automatically uses the wrist heart rate monitor unless you pair an external heart rate monitor."

https://www8.garmin.com/manuals/webhelp/GUID-0221611A-992D-495E-8DED-1DD448F7A066/EN-US/GUID-AB9A0CB2-FA4B-4AD0-894B-B4B6808642A7.html

Is this only true during activity recording? I.e. the internal optical HRM is always using during 24/7 mode, but the watch will use an external HRM if it's present during activity recording mode.

If so, what should I do during a cycling activity when I'm also using an Edge 1040? The normal 24/7 heart rate readings from the optical sensor are fine for 24/7 recording, but are very inaccurate (off by 70-80 bpm) during an activity. 

Hopefully I don't need to dual record (watch and Edge) to get the most accurate heart rate recorded on the watch during a cycling activity.

Thanks

This is incredibly helpful, thank you! One last question: will my Body Battery, Training Readiness, and other metrics that are exclusive to the 965 use the inaccurate heart rate data recorded by the 24/7 optical mode, or will it pull in the more accurate data from the external HRM after my Edge 1040 syncs (i.e. is this covered by Unified Training Status)?

Thanks

During the activities it will use external HRM data. Otherwise the data from the internal Sensor. 

the wrist HR (internal) is not inaccurate. in fact, this is far best wrist HR in garmin watches (even within the elevate V4 series). 

it is lagged, though, with several seconds, and probably won't record sharp changes in HR. however, this won't affect the 24/7 reading, because in the daily recording targets (stress -> body battery, resting HR, nightly HRV) all these particularities do not really matter.

In my experience, the wrist optical HR sensor is very close to a chest strap when the watch is actually recording an activity, but in non-activity mode (referred to as 24/7 mode above), it's 70-80bpm different than a chest strap.

I've read that during activity recording it uses a more-sensitive (and higher power consumption) mode, which is why it's more accurate compared to 24/7. Would love for Garmin to confirm this.

in non stress situations (such as not exercising, resting, sleeping, during normal life) your heart rate goes up and down continuously as you breath in and out, so there is really no point to have a higher sampling rate (otherwise you could end up with a pulsating HR value) (also, you HR is lower in normal life, so the less frequent sampling makes sense).

because of this, you'd need to average out the reading through time to get reasonably representing HR and you can absolutely do that with less sampling rate.

however, the stress level is based on HRV and you'd need precise RR intervals for that, so the watch goes a higher sampling rate mode from time to time to assess that (you can check if you go to the stress glance, the light will run continuously, instead of flashing).

I don't think that this watch is designed or capable handling HRs outside of normal daily HR range (up to ~100) in the 24 hour recording.

One workaround could be to start an activity - while you can go back to the watch face, it will revert back to the activity screen after a while, so it is not a 100% solution for that.

I'd be curious, though, whether any other watch is capable of that - probably yes.