820 Poor Altimeter Accuracy

Same here. Since the last update the altimeter has intermittently shown wildly inaccurate gradient data whilst riding in the UK & France. When I analyse the ride in ST3mobi afterwards, the altitude data seems to be correct however.

I too would like to see a fix for this, as I depend on seeing accurate gradient data whilst riding. 

Does ST3 correct the elevation data? 

I have the same issue: poor readings since the last upgrade. Today I started at 1208 meter, cycled upwards to 1510 meter with at least three steep ascents and descents in between. At 1510 meter, the altimeter should have stated at least 302 meter. Plus another 100 extra or so for the extra ascents and descents. However, at 1510 meter altitude my total ascent according to the Garmin 820 edge was a mere 216 meter. That is a massive deviation...!

Plus: this didn't occur until after the update, so there's something in the update that's incorrect.

Apology: double posted...

I recently noticed the the same problem. The altimeter works fine, showing correct altitude, but the Total Ascent of the ride is very incorrect.

For example, after climbing from 700 meters to 1700 meters altitude, with some small descents in between, the Total Ascent was supposed to be minimum 1000 meters, but it was like 600 meters only. The Total Ascent for the whole ride was 800 meters, while my friends had 1400-1500 meters (also with Garmin Edge, 820, 530). The same day, another ride, same problem.
I think it's because of the latest update...
Please fix ASAP, this is totally wrong. 

Hi any update or fix this issue is forcing a sale of a new unit for me. Im easily 15 to 25% down on total gain compared to ryding buddys and my old 510.

 Do the other units suffer this delay in accumulation?

I have been riding with both an 800 and an 820 for almost a year.  Many of these rides were also recorded on an ancient Ciclosport 436 computer, in fact the 800 overlaps the ciclo for 8 years. My gut feeling based on a decade of riding is that the Ciclo gave the most accurate cumulative climb of all altimeter-based products, and the Garmins reported climb totals a bit higher. 

I read all of my Garmin and ciclo ride data into R and did a quick analysis which showed that for my tiny sample of 1 Edge 800 and 1 Edge 820, the 820 came in at less than 1 percent less climb than the 800 for 142 rides recorded by both, and there was at least 1 glitch in there where one of the computers missed a chunk of the ride, so I would say the difference is probably even smaller.  I compared the 800 to the ciclo computer for 1036 rides with data for both, and find that on average the garmin overstated the climb by about 12 percent.

I have not noticed a pattern to altimeter accuracy with any releases.  If I get a few spare moments I can check.

What I have noticed is the altimeter seems to work well it is just the storing of accumulation that seems to lag and jump in blocks. 

There is a road i ride that is a long decent with some punchy little climbs you get out of the saddle for and it is approx. 5 Kilometer in length. It doen not record any elevation on roads like this.

My unit only is accurate if i do a large straight up climb after that by the time it regestars a decent I am usually climbing again and it does not add this lag to my accumulation.

I have had three 820 replacements  from amazon and each unit has been consistantly bad in this respect.

The terrain I cycle is 450 m climb then descent avg in Dublin wicklow mountains

Same here, Edge 820 permanently measures 10-20% too little altitude. I think this happens after a firmware upgrade.