Does what it says on the tin. This is a basic barometric pressure altimeter. Uses your Android device's built-in barometer to implement a standard pressure altimeter. Only works on devices with barometers.
No ads. No nonsense.
Great for hikers or anybody else who would like to know their elevation.
This is what is known in aviation as a "sensitive altimeter", meaning that altitude is calibrated based on a sea-level reference pressure. Touch the altimeter face to bring up the Kollsman adjustment window. Enter the current sea-level pressure (altimeter setting) to calibrate the altimeter. OR, enter the known local elevation to get the altimeter setting.
If you don't know the current altimeter setting, use 29.92.
See Wikipedia for more information about sensitive altimeters and how they're used: https://en.wikipedia.org/wiki/Altimeter. Aviation altimeter settings can be obtained from aviation weather reports (see https://en.wikipedia.org/wiki/METAR) and airport information broadcasts (https://en.wikipedia.org/wiki/Atis) if you have an aircraft-band radio.
Pro-tip: use the Kollsman window to set the local elevation to zero, to get the local barometric pressure.
Preferences allow you to select altitude (meters or feet), pressure units (inches mercury or millibars), screen orientation, and keep screen on.
Not approved for aviation use. Compare to a real altimeter before you even think of using this, even as a backup.