Experiment Relating to the Vertical Component of the Earth's Field
©Brooke Clarke 2003 - 2007
I used a Suunto Vector Wrist
Computer (electronic based compass) for this experiment since a
needle type compass will jam if it is turned on it's side.
- I calibrated my Suunto VECTOR
Watch - altimeter - barometer -thermometer- level by following
procedure in the manual which involves rotating the watch 360 degrees
holding it level.
- About 30 feet from the house a plastic lawn table was turned
side was pointing to magnetic north.
- If the compass is held level and parallel to the four sides it
0, 90, 180 and 270 degrees. The test is to see what happens to
readings if the compass is tilted so that 12:00 o'clock is pointed
up or straight down.
- At the 0 degree starting position the reading pointing straight
180 and down is 0.
- At the 90 deg starting position the reading pointing straight up
150 and down is 37.
- At the 180 deg starting position the reading pointing straight up
175 and down is 300.
- At the 270 deg starting position the reading pointing straight up
210 and down is 330.
Earth's Field at my Location
Values of Magnetic Field Properties - I
the field at my location:
39.19 deg N, 123.16 deg W and about 1,000 ft elevation on 9/19/1999
D 16d 5.4m - magnetic declination
I 62d 28.7m - magnetic inclination (dip) measured
from horizontal! i.e. it's about 38 deg away from vertical
H 23,376 nt - horizontal component (this is what
a normal compass uses) about 1/2 the total field
X 22,460 nt - True rotational North component
Y 6,479 nt - East component
Z 44,862 nt - vertical component
F 50,587 nt - Total vector (SQRT(X*X + Y*Y + Z*Z)
17 Nov. 2003
This procedure places one of the sensors so it sees the maximum value
of the Earth's field and the other sensor is at right angles to the
field and so does not see it, unless it's disturbed.
Leveled the tripod of a 60GT telescope and inserted a 2" PVC pile where
the telescope usually goes. With the pipe level rotated the
azimuth for a reading of 90 degrees on the Suunto compass.
Note with the Suunto watch on your right wrist and your
arm in front of your chest, like when you read it, it will indicate
North if you're facing North. That's the same as your forearm is
on an East - West line. So when the watch is strapped to a pipe
that pointing North - South it will indicate either East or West, i.e.
Now the watch is rotated 90 degrees around the pipe so the face is now
on one side of the pipe.
Then the elevation is changed until the reading comes back to 90
Now one of the internal sensors is aligned with the
Earth's magnetic field and the other sensor is at right angles to the
Earth's filed. This can be confirmed by rotating the watch on the
pipe. In any position it reads 90 degrees +/- a degree.
Now if an Oldsmobile Intrigue is parked with the car centerline about 9
feet from the compass and the compass rotated about the pipe until the
angle is furthermost from 90 degrees, this at about a 45 degree angle,
then the compass reads 71 degrees.
This means that the car is disturbing the field at right angles to the
main field and this is what could be used for a magnetic signature.
If the total field is 50,587 nT along the centerline of the pipe then
for an indication of 71 degrees the field across from the pipe and at
about a 45 degree angle relative to the ground (don't know how to
explain that, but see the photo) then cross field is
Cross field / 50587 = TAN (90 - 71)
Cross field = 17,418 nT or 34.4 % of the Earth's field.
If the car is moved so that the center line is 12 feet from the compass
it reads 82 degrees, still at about 45 degree rotation on the pipe.
100 * TAN(90 - 82) = 14 % of the Earth's field.
It should be possible to orient the compass so that both
sensors are at right angles to the Earth's field, i.e. they would both
be reading no field under normal conditions. But I need to
scratch my head to figure out how to get there with a compass output,
not individual sensor outputs.
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