3ricj thinks we should use one of these (which he has)

http://www.garmin.com/products/gps35/spec.html

http://www.garmin.com/products/gps35/

We have model: GPS35-HVS

which, per the cheat sheet, supports high alt:

http://showcase.netins.net/web/wallio/GPSrcvrsvs60kft.htm

It's weight is 3.88oz minus cable.