Does HR accuracy vary depending on watch version (s, standard and x)

The bigger the watch the poorer the OHR performance will be. People neglect that bigger means more movement on your wrist = poorer performance. The OHR devalue are identical but form factor really matters, smaller will be more accurate.

But to ensure better OHR performance the watch needs to be further away from the wrist bone to ensure contact with the skin.

My F7 has same poor OHR accuracy as F6Pro. Tacx ride without watch activity and with Polar H10. HR from chest strap 140-150, the watch shows 70-80. Tried everything, tighten/loosen, inner wrist, LR hand, starting activity on watch, nothing helped. Maybe I have bad anatomy.

I experienced this too within the first few minutes starting a workout. I own a 7s, on a 15cm/6inch wrist size. 

I also remeber those problems in the beginning of the 6s era. So maybe they haven't gotten it right with firmware till now. Problem disappeared with 6s someday with an update. 

And I do also believe watch size does really matter. I think it is a combination of watch size and weight. A high weight on a smaller watch also isn't good for HR accuracy, as is a light but too big watch. I think the smaller AND lighter a watch the more accurate HR gets. But firmware has to do it's part too. 

Io ho provato per un periodo...venu 2 (versione da 45 e 40) venu sq,fenix 7s e ora indosso un'instinct 2s...tra tutti la rilevazione risulta piu' accurata sull'instinct,non sembra predere un battito,sia durante le normali attivita' che anche in allenamento!!

Il venu 2 e sempre stato anche lui molto preciso,questo fino a qualche aggiornamento fa'...da li in poi ha iniziato a sottostimare la freguenza cardica sia a riposo che spesso e volentieri anche in allenamento,sembra che comunque non riescano a risolvere questo problema,nonostante vi siano poi stati altri aggiornamenti.

Fenix 7s preciso nella rilevazione,ma forse e una mia impressione...ma sembra che sia pero' piu' lento nel notare un'aumento veloce dei battiti,questo rispetto appunto all'instinct...i sensori di freguenza cardiaca sono gli stessi sia sul venu 2 sia sul fenix 7 e sia sull'instinct 2,a questo punto mi viene da pensare che in base al dispositivo,cambi il software che raccoglie e elabora i dati del sensore!!!

I don't speak your language... 

here you go

I tried for a while ... venu 2 (version 45 and 40) venu sq, fenix 7s and now I'm wearing an instinct 2s ... of all the detection is more accurate on instinct, it doesn't seem to catch a beat , both during normal activities and also in training !!

Venu 2 has always been very precise too, this until a few updates ago ... from then on he began to underestimate the heart rate both at rest and often and willingly also in training, it seems that they cannot solve anyway this problem, although there have been other updates since.

Fenix 7s accurate in the detection, but perhaps it is my impression ... but it seems that it is however slower in noticing a fast increase in beats, this precisely compared to instinct ... the heart rate sensors are the same both on the venu 2 and on the fenix 7 and on the instinct 2, at this point I think that depending on the device, you change the software that collects and processes the sensor data !!!