I installed the app "androsensor" and it shows the actual local air pressure in mbars (hPa) with two decimal places. If the phone ist not moved the displayed value fluctuates by approx. +/- 0.05 hPa which I consider surprisingly precise. If converted to altitude at elevations below 1000m amsl the fluctuations correspond to approx +/- 45cm.
As you say the precision is fairly impresive. With a bit of filtering over the raw readings I use it to record the altitude in to 10 cm in my biking app IpBike. It means I can get fairly good gradient numbers when combined with an ANT+ speed sensor. Far better than you could get with a GPS only solution.
