I've published Bruce's 2009 article previously, but
here it is again.  In addition Mark Graham's
article.

Flytec (6030, 6020, 5030 and 5020) and Bräuniger (Compeo and
Competino series) are comprehensive flight computers that are combined GPS and
altimeters. They make available to the track log both GPS height referenced to
the geoid, and barometric altitude referenced to standard pressure 1013.25hPa.
The Instrument has two barometric altimeters (alti1 and alti2) which can be
independently set and user fields can be set to display GPS height or barometric
altitude. The barometric altitude displayed can be with respect to the user set
QNH or QNE. Bear in mind that if the unit is set with QNH, then the track log
still contains the information with respect to 1013.25hPa (QNE). It is good that
all of the instruments record altitude with respect to the same reference, but
is not necessarily the actual amsl for the day. It is in fact the Pressure
Altitude and is the information required for avoiding airspace flight above the
transition layer. Final glide calculations are made using alti1 so this is best
set to QNH.

6. 1 On days when the restrictions are altitude amsl then all of the instruments
should be set to the lowest predicted QNH for the day for the region of the task
(Garmins must have altimeter calibration set to manual), this should be
announced on the task board.

...

The scorer will need to take the 1013.25hPa derived traces (Flytecs/Bräunigers)
and add the relevant 1013.25 - QNH * 27ft/hPa to get the actual flight altitude.
The scoring software could be made to automatically correct these traces using
the QNH previously announced. For the instruments that record pressure relative
to QNH, it may be necessary to stipulate that the track log is unbroken
throughout the flight. It is feasible that the instrument can be switched off in
flight and the altimeter calibration changed in order to cheat, though why
anyone would want to cheat is beyond me.

6. 2 On days when the height restriction is FL, then there are two options:
Option 1: All of the instruments should be set to 1013.25hPa, QNE. The
barometric data recorded by all of the instruments will have a common 1013.25hPa
reference making life easier for the scorer. The instruments with only one
altimeter display (eg the Aircotecs) will display Pressure Altitude (good for
avoiding airspace) but there will be a problem with the final glide calculator
because zero feet will not necessarily be at sea level.

This has got to be made a lot easier for the pilot and for the
scorekeeper. The actual values used at the pre-Worlds were never communicated to
the pilots. I suggest that pilots with Compeo+'s and Flytec 6030's just set
their altitude at launch by pressing the left soft button.

Thanks to Ed at Cross Country Magazine.