單項選擇題The variation for most given areas undergoes（）change，the amount of which is also noted on charts.

A.an annual
B.a constant
C.a variable
D.an unstable


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1.單項選擇題The quadrantal spheres are used to（）.

A.Remove deviation on the intercardinal headings
B.Remove deviation on the cardinal compass headings
C.Remove heeling error
D.Compensate for induced magnetism in vertical soft iron

2.單項選擇題The MOST important feature of the material used for making the binnacle of a standard magnetic compass is that it is（）.

A.nonmagnetic
B.weatherproof
C.corrosion resistant
D.capable of being permanently affixed to the vessel

3.單項選擇題The most accurate method of determining gyrocompass error while underway is by（）.

A.Comparing the gyro azimuth of a celestial body with the computed azimuth of the body
B.Comparing the gyro heading with the magnetic compass heading
C.Determining from the chart the course made good between celestial fixes
D.It cannot be determined accurately at sea due to drift of unknown currents

4.單項選擇題The magnetism in the various structures of a ship changing as a result of cruising，vibration，or aging is termed（）.

A.permanent magnetism
B.subpermanent magnetism
C.induced magnetism
D.variable magnetism

5.單項選擇題The line which connects the points of zero magnetic dip is（）.

A.An agonic line
B.The magnetic equator
C.A magnetic meridian
D.All of the above