Big disparity in Heart Rate between 4 and 4s

Try again with both on the same wrist.

I am right handed and wear mine on my left wrist, but i noticed I get a MUCH more reliable reading, both for exercise and while sleeping with SPO2 if I wear the watch on my right wrist. I don't understand why, my skin should be the same on both wrists....

Many thx. I'll give that a try.

Thx for your response.

I don't understand why the readings should be markedly different between my left wrist and right wrist. It makes me question the reliably of the data.

Also, my Vivoative 4 never shows any deep sleep for me while my Vivosport always does. Go figure.

I'm thinking seriously about returning it. As much as I like the look and functions of the watch, it is just a toy if the data it produces can't be trusted.

One thing to consider is your heart is closer to your left arm than the right.  That's why using the same arm for both can make a difference.

You're not a doctor are you Jim ;-)

Although your heart is normally on the left, and the left side of the heart pumps the blood around the body,  the aorta exits the heart heading towards the right and artery to the right arm is in the first group of big arteries branching off the aorta, with the left arm artery in third position.

Anatomy lesson now over,  and also completely irrelevant since closeness to heart has very little to do with whether a pulse based HRM tracks heart rate accurately. 

What is more relevant is local blood flow under the sensor. This may be higher on the dominant arm (which trends to have more developed musculature) and lower if too bony close to the wrist. Previous injury may also influence how much soft tissue there is between skin and bone.  In my own case, I am right handed and normally wear the watch on my left. I have also had several childhood forearm fractures,  which means my left arm is a bit skinnier near the wrist than my right. At low heat rates the VA4 tracks pretty closely to an external chest strap HRM (detects heart beats electrically rather than by pulse)., but during vigorous exercise it tends to under read. If I really care about accurate heart rate tracking, I tend to use the chest strap. I've previously found that I get slightly better heart rate (pulse) tracking during sleep if swap the watch to my right arm.

Your suggestion of trying with VA4 and 4S on same am is a good one, but I would ideally run a couple of tests with proximty to wrist reversed in between. I'd also suggest trying opposite arms, with reversed sides in between.

I'd be most interested in what you find .... I suspect  that the 4S may read higher when on the dominant am, or further from the wrist. 

Let us know please! 

I know I see variations if I wear a garmin on the left and on the right.  And switching wrists, the same difference can be seen based on wrist, not watch.

Life lesson now over...

Interesting development: today I put the Vivo 4 near my hand on my left wrist (I'm right-handed) and the Vivo 4s next to it up the arm. When I was doing a warm-up walk, there was still a 15 - 20 point HR difference between the two units. Then when I pressed the start button on both watches to start the run, there was a brief message on the Vivo 4 that said something like HR+ 303030; it appeared to be an update. After that, the two watches synced very closely on the heart rate and I didn't get the abnormally high readings on the Vivo 4 during the first mile of my run. 

I don't know what happened but it seemed to fix the problem.

There is still a five-point variance between the two oxygen readings (96 and 91) with both units on my left wrist.

Thx for the feedback! I think I will get and try a chest strap to check the HR readings. I'm not sure the Oxygen sensor is all that accurate but I don't know how to check that.

I think the oxygen sensor is pretty inaccurate. I have a finger pulseoximeter that is very accurate and the VA4 is always 5-8% off. It isn’t worth the battery loss imo unless looking at general trends. 

I did notice that the hr sensor is very slow to respond and inaccurate when I am up and moving around but seems to correct itself and be much better if I actually start an activity. Just some observations.