BJen wrote:
GPS altitude is relatively poor, but is one
option for getting current altitude info to the PDA. I
suppose you could input it manually, but that doesn't sound
practical. The best is a pressure sensor, but that would
mean getting altitude info from either a flight computer
(same as the airspeed problem above) or a Flight Recorder
that outputs its pressure altitude. Does the Volkslogger
give pressure alt to the PDA? Reading between the lines on
the PDA summaries I think it does.

GPS altitude is a more accurate indication of your actual (geometric)
altitude above sea level, so a lot of people use GPS altitude for final
glide, even if they have a flight computer or recorder that outputs
pressure altitude. Pressure altitude provides a more accurate short
term (a few minutes or less) indication of change in altitude.

BTW, some of the newer versions of PDA programs contain an internal map
of the ground elevation, so they can display your altitude above ground.
Some now figure your final glide altitude needed with consideration of
the ground elevations (i.e. mountains) between your current position and
the destination.

For vario functions, it looks like it would need access to
TE. That's only available from a vario or flight computer.
I suppose it could fake it with altitude info for non-TE or
pseudo TE using wind and ground speed info. Do any do this?

Using GPS altitude only, the climb rate averaged over 30 seconds or so
is fairly accurate most of the time. Some PDA programs do this, some
also try to account for total energy as you suggest, most calculate an
average thermal climb rate, which is usually quite accurate.

For STF, it again needs TE from a vario or flight computer,
but I suppose it could fake it as above.

Does that sound right?

Yes.

Marc