Discrepancy in elevation data

Which source of elevation data is correct? I did a short training ride this morning doing steady hill reps on a local hill. I had two Garmins on the bike (520 and 820). When I got back to the house, I uploaded my ride data and analysed it. Here’s the elevation data from various websites and the two devices:

Garmin 520: 2,854 ft
Garmin 820: 2,772 ft
Strava (data from 820): 2,772 ft
Ride with GPS (data from 820): 2,830 ft
TrainingPeaks (data from 520): 2,854 ft
TrainingPeaks (data from 820): 2,772 ft
Trainer Road (data auto-synched from Strava): 2,877 ft

As an experiment, I used Strava’s elevation correction, and it changed from 2,772 ft to 2,788 ft.

Here’s part of the reply made by someone from TR on a previous thread about bad elevation data from outdoor rides:

"Sadly, there is no way to correct the elevation data within TrainerRoad at this time :pensive:. Strava and Garmin Connect both use a mapping correction software that we simply do not have at this time. Incorporating mapping software is something we may do in the future, but due to its high cost of implementation, it is a fairly low priority. "

How and from where did TR get a different elevation value to the same ride, when my TR account auto-synchs with my Strava account? If TR simply imports ride data from Strava, shouldn’t the two sets of data be virtually identical?

So, which of all the different elevation readings shown above is the correct one? Any ideas?

It’s my understanding that TR is simply taking the raw file from your Garmin but through Strava and displaying that data while Strava is doing some post processing before displaying it. So Strava will attempt to use both your Garmin’s collected elevation data and know elevation data from their mapping and reconcile the two in case your garmin’s data is way off due to weather patterns, dirt stuck in the barometric sensor, etc.

Your numbers are all within +/- 5% so for me I would say they are all correct within an acceptable margin of error. You’re not using super precise measuring tools so that’s just something that you’ll have to deal with I think.

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Thanks for the reply. Much appreciated.