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Magnetic Compass Deviation Tables
Purpose
The purpose of the magnetic compass deviation tables, commonly
refered to as "deviation tables," is to provide a means of knowing the
deviation of the magnetic compass for any heading. This information is
crucial to safe navigation if the gyrocompass fails.
Table
Composition
The figure on the right is an
example of a deviation table. The
top portion of the table contains the
name of the ship, location of the
compass (pilothouse), binnacle type,
and compass type.
The middle section of the table
contains the ship’s heading and
deviation data.
Example: You want to steer course
090° magnetic. By inspecting the
table for ship’s heading 090°, you’ll
notice that the deviation is equal to
1.0° West with DG OFF (DG is an
abbreviation for degaussing) and
1.5° West with DG ON. To make
good 090°, you would have to
actually steer course 091°.
The bottom portion of the table
contains information on magnet and
flinders bar placement that corrects
for excessive deviations.
Figure 2-8. Magnetic compass
deviation table.
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