In the Oct, Nov, or Dec 2008 issue of Nuts and Volts
they had an article about a device that will tell
you what your current alittude is. Its is called
"ZLog Altimeter". Their web site is
The hardware software can be used either to take a reading every xx milliseconds or to log min and max values.
I should check it out and find out what chip the software used to measure the altitude.
The product costs $70.