I've just ordered a pressure sensor for my RPi. Another thing to add to my chart.

You need to put a page on your website with one of these, linked to the pressure history:

Kos is right, they use it for a more accurate altitude reading. If you compare results from tracking a bike ride (for example) on a phone without the barometer it's quite a lot different to with.

Maybe you should adapt it to read pressure between two surfaces - like, say, between a speaker and what it's sitting on  :O)

That is pretty impressively accurate for something that is stuffed in a mobile phone. Haven't all these sensors in mobiles made gyros and accelerometers and such cheaper for other things?