> How would I use the API to pull the highest altitude of a call over the past 24 hours?
Unfortunately the API does not provide such a function. For locations it
only provides the most recent position (and it's altitude, etc).
You can manually download a machine-readable export (KML,CSV,JSON,XML) for
the past 24 hours using the http://aprs.fi/export/ tool, but that's not an
API which you could use all the time in an automated fashion.
- Hessu