Altimeter Free is a travel and navigation app developed by SpeedyMarks for Android devices. It uses GPS or the built-in barometer to determine the user's current elevation on earth, providing accurate altitude measurements both indoors and outdoors.

The app allows users to set a base altitude as a starting point and get the altitude difference for activities such as hiking or biking. It also offers calibration of the barometer altitude, connecting the current air pressure to the current altitude. Users can calibrate with the help of GPS, the standard sea level air pressure, or to any altitude they want.

Moreover, Altimeter Free provides time difference to the last calibration and a warning when it is time to calibrate. The app also features the option to switch between metric and imperial units.

While the app is ad-supported and does not support watch devices, it is a useful tool for anyone in need of accurate altitude measurements, whether for outdoor activities or indoor navigation.