单项选择题
A.accurate only in the Polar regions
B.accurate electronic servomechanisms
C.hand operated
D.accurate only if the vessel is underway
单项选择题 How is variation indicated on a small-scale nautical chart?（）.
单项选择题 If（）is shut down for an extended time optimum position fixing will take up to 2 hours after power is reapplied．
单项选择题 If a magnetic compass is not affected by any magnetic field other than the Earth’s，which statement is TRUE?（）.