John Jones wrote:
Basically, do with software and the GPS data the 'circle
shifting' we do in our head.

Can this be programed into a PDA?

Themi also incorporates a variometer. Given the short-term errors in
GPS altitude, you can't get close enough to an accurate instantaneous
climb rate indication to be able to do the "circle shifting" trick using
GPS alone. Plus, I believe the Themi algorithm is patented in the EU
and US...

Marc