SAR Fundamentals/Compass practical and pacing

00:00

3 min

Introduction

Introduce topic title

Introduce Instructor

Present Objectives

00:03

Review - declination

• Magnetic north is not the same as true north
• point out the approximate direction of true north and magnetic north
• The difference between the two is called declination
• In our part of the world magnetic north is to the east of north, so we have EAST declination
• Declination changes each year as the north magnetic pole moves

• Give declination for lesson location to the nearest degree (ignore seconds)
• We should always ask what the declination is for our search area

Setting declination

• The needle points to magnetic north
• But we want the directions on the compass bezel to show directions relative to true north
• We do that by setting declination on the compass
• We use the key on the lanyard to move the bed
• point out how to read the declination a compass is set at
• On most compasses, each tick represents 2 degrees, so odd numbers are half way between ticks
• point out which side is EAST declination and which is WEST
• Have each student set their declination to zero and then back to the correct declination for this location
• Check that each student has correctly set declination

Review - compass failures

• avoid metal
  • don't hold compass close to your belt buckle
  • don't stand near vehicle, metal building
• avoid magnetic fields
  • don't stand underneath high power lines

Holding compass

• about arm's length away from you
  • don't have lanyard around your neck
• hold the compass about at eye level
• hold the compass level
• demonstrate

Sighting

• sighting requires that you have several things working at once.
• close one eye
• fold the mirror so you can see all of the bezel in it
  • when you hold the mirror away from you, you're looking in the mirror; you're not looking down at the bezel directly
• make sure you're holding the compass level
• make sure you see the center line in the mirror slices through the middle of the needle
• use the sighting notch at the top of the mirror center line to spot your target
  • you may have to raise or lower the compass slightly to bring the target into view
  • some compasses also have a sighting notch at the bottom of the mirror center line
• RECHECK you have all things correct at the same time:
  1. one eye closed
  2. compass level
  3. can see all of bezel in mirror
  4. mirror center line through needle center
  5. can see target in notch
• demonstrate
• have each student sight on an object on the far distance; have them verbally confirm each of the sighting requirements
  • Because you can't put your head where the student's head is, you won't be able to check all of their sighting requirements, but can check whether they are holding compass level, have one eye closed. You can approximate the others by looking over their shoulder.

Aligning needle

• the north pointing end of the needle is painted red
• the "bed" of the needle is on the plastic underneath and points slightly to the east of North on the bezel
  • because we set EAST declination
• we want to put the "red to the bed"
• two ways
  • rotate the compass until they line up
  • rotate the bezel until they line up
• demonstrate both methods
  • looking down on compass, not using mirror
• have each student align their needles using both methods
• when the the needle is aligned, the directions on the bezel are the directions relative to True North

needle parallax

• it's easy to align the needle when looking straight down
• if you look sideways it's harder
  • called parallax
• we need to be able to do this so that we can "sight" at the same time as aligning the needle
• demonstrate
  • set direction of travel on bezel to East (90 degrees)
  • fold mirror flat (so it can be ignored)
  • hold the mirror at eye level so you are looking obliquely at the compass surface
  • demonstrate rotating your body until the needles align
• have students do the same
• have student check their alignment by then looking straight down on needle
• trick is NOT to try to get the tip of the needle in the middle of the bed
• trick is to try to get the edge of the needle parallel with the edge of the bed
• have students retry until they can get proper alignment looking

• have students try again with direction of travel set to North (0 degrees)
• This is much easier because we're looking along the needle length
• direction near north and south are easy to align, near east or west are harder

• when we're using bearings we need to use the mirror
• the mirror makes it more difficult to align the mirror
• because we're looking sideways at the needle, not straight down

Reading a bearing

• reading bearing
  • rotating barrel
  • "red to the bed"
  • parallax problem
    • parallel needle edge, not needle in the middle
  • practice reading bearings to several objects
  • vary distance and note differences in error

• walking a bearing
  • setting bearing
  • how far to look
  • practice finding destinations at several bearings

3/ Pacing

• Step is one foot to the opposite
• Pace is one foot to the same foot (two steps)

• counting your pace

• measure your pace in 10m

• calculating distance from paces

• calculating paces from distance

4/ Exercises: bearings

• hand-out: Pacing and Traverse

5/ Advance

As they come up in discussion, describe:

• back bearings

• offsets