Barometric altimeter on 'future' Freerunner ?

[adam at laurasteele.net]

GPS does give relatively accurate altitude/speed but it does have  
error and is nowhere near as accurate as a calibrate barometer (since  
an aircraft altimeter is just a barometer with a different face).

Assuming someone has a data plan you can get the barometric pressure  
from a nearby airport (most have a weather station, all data is pooled  
by the FAA online**). Wouldn't be sure about other countries but I bet  
France/most sizable would have something similar. That or you could  
assume the "standard" 29.92 in/Hg and 1000ft per 1 in/Hg.

An even more desperate thing you could do is call 1800-WX-BRIEF and  
ask what the baro is at a local airport.

**They also maintain a very detailed list of all airports available as  
an XLS file.