Pace Calibration (instructions below)
|Paces 1st||Paces 2nd||Paces 3rd||Paces 4th||Sum (for 100m)||paces/meter||meters/pace||paces/mile|
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Compass Calibration sidewalk azimuth instructions below)
|Mag. Azimuth 1||Mag. Azimuth 2||Mag. Azimuth 3||Average Mag. Az||True Az ( = Mag Az + E decl)|
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Dead Reckoned Open Traverse Data (see instructions)
|Leg||Distance (meters)||Azimuth (true)||Paces (=m*p/m)||Azimuth (mag) (= true - E decl)|
|1||40||220|| || |
|2||25||312|| || |
|3||65||260|| || |
Assessing the results
Sketch the distribution of the markers on the back of this sheet.
|Did we do better with measuring the angles or measuring the distances? Why do you think so?|
The objective of this exercise is to provide an introduction to using a compass and pacing in land navigation. Secondary objectives are to examine the compounding of measurement errors when we are measuring angles (with an orienteering compass) and distances (using pacing) for a dead reckoning course.
The orienteering compass has three main parts: (1) a base plate with a direction arrow, (2) a rotating capsule with an alignment arrow, a declination scale, and an azimuth angle scale, and (3) the needle.
To take an azimuth: hold the compass so that the needle can rotate freely, rotate the capsule so that "N" aligns with the north end of the needle, keeping those aligned, rotate the base plate to aim the direction arrow at the target, read the azimuth from the scale at the direction arrow.
To follow an azimuth: align the azimuth with the direction arrow, orient the whole compass so that the N and needle align, follow the direction arrow.
Several cautions. (1) Azimuths can be relative to several different "Norths": 'Magnetic' or 'True'. The difference between them is the declination. Your compass can probably be adjusted to correct for declination by rotating the capsule's alignment arrow relative to its degree scale or by aligning the needle with a declination scale. The declination in Honolulu (30 Jan 2013) is 9 degrees 42 minutes East and moving 2 minutes west per year, so (rounding to fit the instrument) the needle points about 10 degrees east of true north. Align the needle with the "10 degress East declination" mark on the capsule (rather than the arrow) and your azimuths will be "true". Alternatively, to convert true azimuths to magnetic azimuths, subtract east declinations and add west ones; one mnemonic is: "east is least, west is best". NOAA's National Geophysical Data Center has an online tool for estimating the current declination, see: www.ngdc.noaa.gov/geomagmodels/Declination.jsp . (2) The scale of degrees is marked in fairly coarse increments; 2-degrees on the Suunto A-10. More precise measurements can be made with a compass offering finer increments, a larger bezel, a longer and finer sighting mechanism, and perhaps a sighting mirror such as are found on a Brunton Pocket Transit (tm).
A 25 meter distance has been marked on the sidewalk outside of our classroom (look for "104"s on the concrete). One is at a 'crack' near the front stairs of Crawford Hall. The other is along the edge of the sidewalk toward the Architecture Building (west).
Walk the course four times counting your paces each time. Estimate partial paces at the end of each pass. Calculate your average pace length (in meters) and your number of paces per meter.
E.g., Suppose that for four trials one gets: 15.1, 14.8, 15.1, and 15.0 paces over the 25 m course. They sum to 60.0 paces and average to 15.000 paces for 25 meters (i.e., 60.0 / 4.0 = 15.0). That indicates paces of about 1.66 meters (i.e., 25 meters / 15.0 paces = 1.667 meters/pace). Alternatively, you could calculate paces/meter, 15 paces / 25 meters = 0.6 paces/meter. Multiply your paces per meter by 1609.34 meters/mile to get your number of paces per mile for when that is more convenient. Carrying these calculations to centimeters is overly precise.
Practice can make you a more consistent pacer. One can be easily distracted from counting but practice helps there too, as might a mechanical counter, a knoted string, or a set of pebbles to transfer from hand to hand or pocket to pocket.
To provide some means of comparing the calibration of your compasses, take the azimuth of the pace-scaling course. I.e, toward the west along the edge of the sidewalk. Do it three times to see how consistent you and your compass are. Average the three. Note that the average of cyclic measurements are tricky; if you have azimuths that straddle 0, add 360 to the ones that are just above 0 and if the resulting average is over 360, subtract 360 from it.
Start from the Nina Etkin Memorial plaque (near the sidewalk between Crawford and Hawaii Hall) and follow the short 'open traverse' set of azimuths and distances listed above, placing markers at each of the dead reckoned way points. Note that the azimuths are given from True North and you should convert them to Magnetic for your compass.
Once everyone has placed their markers, sketch their distribution on the back of the answer sheet. In a few words on the sketch map address whether we did better with the angles or the distances? Why?