This altimeter works online and offline. It estimates your elevation with three different methods:
- Using GPS satellites triangulation. No internet connection required, quite accurate with clean sky but works only outdoors and it's slow.
- Using the ground elevation at your current position. Accurate but require internet connection and works only if you are at ground level.
- Using the pressure sensor of your device (if available). If it's available internet connection it calibrates itself on the nearest weather station pressure to improve accuracy.