DAVIS THREE-ARM PROTRACTOR - Manual

#071
TO FIND YOUR POSITION:
1) Select three features that are clearly recognizable
on your chart—for example, a lighthouse, a small
harbor, and a church steeple.
2) Using your hand bearing compass, pelorus, or
sextant, take the bearings of each of the three fea-
tures. Calculate the number of degrees from the
central feature to the feature on the right, and from
the central feature to the feature on the left.
3) Using the stationary arm of the protractor to repre-
sent the central feature and the two rotating arms
to represent the features on either side, set the
arms to the degrees calculated in Step #2 above.
To set degrees, place the long black line of each
rotating arm over the nearest whole degree mark
on the protractor scale. To set minutes, rotate the
arm slightly until the desired number of minutes on
the vernier scale (the scale on the rotating arm)
lines up exactly with a degree mark on the protrac-
tor scale.
4) Without changing the setting of the arms, manipu-
late the protractor on the chart until the long black
line on each arm is over the corresponding land
feature.
5) Mark your position through the center hole of the
protractor.
THREE-ARM PROTRACTOR
INSTRUCTIONS
Note: This product was discontinued in 2003.
3465 Diablo Ave., Hayward, CA 94545 U.S.A.
Phone (510) 732-9229 • Fax (510) 732-9188
[email protected] www.davisnet.com
071_Inst.pdf October 2005