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.
Great for hikers or anybody else who would like to know their elevation.
No ads. No spyware. No nonsense.
Go to settings and set your preferred units: feet or meters; inches of mercury or millibars.
Find out the local altimeter setting (pilots can get this from the nearest airport). This will look something like "29.92" (inches of mercury) or "1013" (millibars). Touch the display to bring up the Kollsman window. Set this to the local altimeter setting on the left. Now you simply look at the display. Altitude is displayed numerically on the left, and via the three hands. The very skinny hand ending with a triangle represents 10,000 feet (or meters), the short fat hand is 1,000 feet, and the long hand is 100 feet. You read it pretty much like a clock.
If you don't know the local altimeter setting, use 29.92.
OR, if you know your altitude and want to find the altimeter setting, use the Kollsman window and just enter your altitude on the right.
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.
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.