The experiment "Pressure" just gives the raw data from the phone's barometer.
Unfortunately, at the time of this writing, the barometer is not found on all phones. For iOS, this sensor can be found on the iPhone 6 and 6s (not iPhone SE or older models), while on Android there have been barometers around a bit longer, but they are mostly found on the more expensive models.
As the pressure sensors in phones are designed to determine the user's vertical location within a building, they usually give surprisingly precise results. Most sensors can easily resolve a height difference of 1 meter, which is about 0.1 hPa = 0.1 mbar.