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Determining Gyro Error by Terrestial Range
Background
An excellent opportunity to check the accuracy of the gyrocompass
presents itself each time a ship enters or departs port. Most harbors will
have at least one set of range markers set. This method of checking a
gyrocompass is often referred to as obtaining a range of opportunity.
To determine gyro error by terrestial range, you should follow the steps
in the table and refer to figure 2-21.
Step
Action
1.
View the range markers through the alidade.
2.
The ship maneuvers "on range" (range markers are in
line.)
3.
"Shoot" (take) a bearing on the range markers while
they are lined up.
Compare the bearing taken against the chart.
4.
Figure 2-21. Determining gyro error by
terrestial range.
Tip
It is also possible to mark a range as it passes down the port or
starboard side of the ship. The steps in the action table are still basically
the same; the exception is that the ship will not maneuver on range.
The bearing taker must shoot the bearing to the range markers the
instant that they are in line. This method is only as accurate as the
experience and ability of the bearing taker.
2-32
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