Altitude so inaccurate is basically useless on 530

I see this issue across multiple devices including Garmin watches, Edge 530 and 1030 units.

Elevation data comes from the air pressure sensor not the GPS.

How do you know the Apple watch is accurate and the Garmin is not?  Does it really matter if the elevation data is off?

Are you really sure Apple watch is accurate? I have pretty good results with Edge 530. Especially when I compare it with my Vivoactive 3.

I see difference between my VioactiveHR and 500, Not been out been out with my 530 yet.
When I selected to use computed/map altitude on Connect and Strava I got a couple of more values.

If you switch on altitude correction in Garmin Connect, how much is your total adjusted by?  For most of my rides its a few %.

I compared other rides with Friends computer and the apple watch were pretty much exactly the same as the suunto computer. I had another ride yesterday - 52km and climb 908m. Friend recorded 899m and we finished at the same altitude where we started. Garmin showed that we only did 235m and my starting altitude was 120m and I finished at 207m - same spot :)

What is your recording rate?  I have an 830 and a power meter so my recording rate is set to 1/sec by default.  My elevation values are very consistent and accurate I think.  If you have yours set to Auto or some longer interval, this might be the problem. 

I notice that the speed graphs in your screenshots at top are very different as well, which might also be a result of your bike having a speed sensor (?) which the watch obviously lacks.  But this could also be a symptom of a recording rate that is too low.

Do you have any kind of case or mount that’s blocking the sensor holes?  Seems odd that you have had two with the same issue.  Mine is accurate against maps and other Garmin devices with barometric recording.  Apple watch 5 is the first with a barometer, earlier use GPS alone which is not accurate.

I ran a test yesterday using my vivoactiveHR, 500, and 530. 
The HR was set to Auto Calibrate - not sure how that works, the altitude never makes sense. Manual calibrations does not seem to help.
For the 500 I have a Location set on my driveway which I guesstimated as 850 from contour lines. When you press start and near that area it will calibrate to that elevation.
For the 530 I had not set one yet, what it showed 870 at the starting point. All where set to 1 second recording.

Vivoactive HR. Start 765, end 764, max 826, min 655, GAIN 417, LOSS 430

Edge 500   Start 854, End 814, Max 949, Min 768, GAIN 512, LOSS 479

Clearly a lot of drift here with the end elevation being 40 ft less than the starting.

Edge 500.  Start 871, End 865, Max 935, Min 755, GAIN 469, LOSS 469.

I then changed the Edge 500 in Connect to map adjusted elevation. It did to change the gain at all.
I then changed the Edge 500 in Strava to map adjust elevation and it changed the gain from 512 to 465

From Strava adjusted map elevation Start 851, End 855, Max 923, Min 750 Gain 465

As I was riding the 530 was would indicate 5-10 ft higher than the 500 during the first part of the ride. Then at some point it was about 20 ft lower for the remainder of the ride.

Based on the fact that the 530 closed and it is close to Strava map adjusted value I declare that it is the accurate  in may case. And both the 500 and vivoHR have serious issues as I had long suspected.

We wanted to make sure that anyone who is seeing elevation inaccuracies on their 530 has viewed the below FAQ. We understand this may not resolve 100% of cases, but it is definitely a good start. 

support.garmin.com/.../