Name: ElevateME - Highest Altitude Accuracy
Rating: 4.8 (13 reviews)
Author: Deiv

This App gets elevation through the internet, so it is useful to calibrate your device or simply to check the altitude.
The application works free, but it is possible to obtain PRO functions, which allow the elevation to be updated automatically every 8 seconds.
The PRO function costs €3.50 and you can obtain the activation code at:
https://www.deivliutaio.com/garminapp/

How the app work:
- The gps position is detected through your device.
- When satelittes is connected your position will be sent to the API server. 
- The Garmin Connect APP on your smartphone will be your proxy, so you must have internet and bluetooth active to use this app.
- You receive your elevation data based on your location.

The Elevation API server used on this APP it's Open Topo Data. Some malfunction on data result may be possible, it's a free and open project.
To obtain the elevation data the API server use Mapzen's terrain tiles are a global DEM dataset, including bathymetry. 
Data is provided at a 1 arc-second resolution, corresponding to a resolution of about 30m at the equator. However, parts of the dataset are interpolated from lower-resolution datasets. 
The resolution of the source datasets is shown on image above.

Open Topo Data elevation API (https://www.opentopodata.org/)