*** Compasses for Night Use ***

Tue Aug 27 10:37:24 1996
Message : #1692280252    From: Markus F Bj|rksten
Address : bjorkste@cc.hut.fi
Subject : Re: Compass Opinion
Org.  : Helsinki University of Technology, Finland

Tritium illumination of needle, fork and arrow is most important in
night navigation when not using lights. Typical compasses only have
phosporescent illumination, which needs to be 'charged' with light
every now and when. Red light, as used at night for conserving night
vision while reading the map, does not charge typical units. The
safety risks of the radioactive tritium are nil unless one intends
to eat the compass :).

Lensatic and mirror compasses are useful for taking accurate bearings
over long distances, as needed in open terrain in good visibility.
These are however usually clumsy (heavy, lidded etc) for taking
frequent bearings as needed in covered terrain or low visibility.
Liquid damped unlidded compasses with transparent plastic base plates
are best for frequent bearings. The needle needs to be fast and stable
for convenient and reliable usage on the move.

Many compasses have too loose rings, which may result in accidental
change of bearing. This is a big problem especially at night when
the dial cannot be seen. A manual step counter is moderately useful,
while 'declination setting' probably is not, as it is trivial to
correct for magnetic north manually. One should make sure, that the
compass works at all ambient temperatures that are needed and that the
needle is balanced for the correct zone.

The US military tritium illuminated lensatic compass is the only
adequately illuminated compass that I have used. It is however not
good for frequent bearings on the move (too heavy for hanging, far
too slow needle).

Typical relatively inexpensive backcountry compasses with transparent
plastic baseplates typically have phosporescent illumination
(Suunto, Silva). The needle is typically not very fast nor stable
making usage on the move frustrating.

Suunto's 'Nato tritium' models (at least M-5NT and RA-69NT) are similar
to typical transparent plastic base backcountry compasses (not a good
needle either), except that they have tritium illumination of the arrow
only, while the fork and needle have ordinary illuminaition. This
is of course a waste of the expensive tritium.

Good quality, and expensive, 'competitive' orienteering compasses by
Suunto and Silva have fast and stable needless for easy usage on the
move, but have no illumination, not even conventional phosphorescent.
These are the best choises for navigation in good illumination.

Unfortunately, as far as I know, there is no adequate compass for
lightless night usage.


Markus Bjorksten

                       ---------------------------