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  • From: Una Smith <una.smith@att.net>
  • To: Mounted search and rescue <msar-riders@lists.ibiblio.org>
  • Subject: Re: [MSAR] compass question
  • Date: Tue, 16 Mar 2010 14:22:42 -0600

Tracy Cartwright wrote:
>I was reading the New Mexico MSAR study guide and it states that
>military or lensatic compasses are not acceptable for their gear
>list. May I ask why?

Study Guide: http://www.nmesc.org/FieldCert_docs/StudyGuide.pdf
Exam sketch: http://www.nmesc.org/FieldCert_docs/FieldCertExamInfo.pdf

Thor's explanation is correct. Those compasses are more complex, more
expensive, larger, more difficult to use with (align with) a map in the
field. But the most direct answer is that New Mexico SAR Field
Certification involves a hands-on test of basic compass use and too
many people using those compasses had difficulties with that part of
the test due to some aspect of these compasses.

I did pass the compass test using a high-end lensatic compass designed
for field geology, but just barely. I had the compass set to the local
declination, so naturally my examiner wanted a magnetic bearing to a
point on the horizon. On this particular compass, declination is set
by a tiny screw that is designed to be difficult to change. At that
moment I did not have on my person a screwdriver tiny enough to reset
the screw, so I had to correct for the declination in my head. Doing
a mental task like this on the spot, while someone is waiting, is not
easy. And because I used to live far east of the zero declination line
and New Mexico is west of it, the mental conversion I used for so many
years does not work and I get confused. My poor brain nearly seized
up on the spot.

Worldwide, orienteers use magnetic north, so that the map and compass
work exactly the same everywhere. Of course, for SAR we use whatever
map is available and often the map is oriented to true north. However,
in general incident command is working with maps while field teams are
working with bearings taken in the field. So field teams use magnetic
north and incident command handles needed corrections for declination.

The Study Guide could be clearer about what compass features are okay
or not. http://www.thecompassstore.com/sighting-compasses.html shows
a large variety of "sighting compasses". Desirable features for SAR
include see-through baseplate, easy declination adjustment, place to
attach a lanyard, and 360 degree bezel. Many but not all compasses
shown have all these features.

Conversely, http://home.comcast.net/~galeso/Catalog.htm shows a wide
variety of orienteering compasses. None of them have a way to adjust
for declination. Furthermore, some of them are so highly simplified
that they have no bearing marks at all, only a north reference line.
Many of these compasses are not suitable for SAR.

Una Smith
New Mexico




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