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Determining the Ship’s Position Using Sextant Angles, Continued
Setting the
Protractor
The movable arms can be set to the nearest minute of arc using the
vernier scale that is inscribed on the movable arms. Use the following
steps when setting the movable arms to a specific angle. Figure 8-22 is
an example of a setting of 12° 18' on the three-arm protractor.
Step
1.
2.
3.
Action
Loosen the clam screw on the arm you are setting.
Move the arm so that the index line is between the degree you want and the
next higher degree.
Adjust the arm so that the vernier mark indicating the minutes of arc you
want is directly in line with the degree mark closest to it.
Note: Make sure you apply the index error correction to angles.
4.
Tighten the clamp screw on the arm.
5.
Repeat steps 1 through 4 on the other arm for the second angle.
Figure 8-22. Setting angle on the three-arm protractor.
8-36
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