USCG USCG NAV
Set 7 • Question #190 of 247
Launch Interactive Practice Room During twilight on 28 December , about 1800 GMT, in DR position LAT 4°00'N, LONG 0°06'W, the sextant altitude (hs) of Venus was 30°46.8'. The height of eye was 36 feet, and the index error was 2.0' on the arc. The temperature was 68°F. The barometer read 1030 mb. Calculate the observed altitude (Ho).
A
Ho 30°35.2'
B
Ho 30°37.1'
C
Ho 30°38.1'
✓ Correct Answer
D
Ho 30°40.3'
USCG NMC Regulatory Explanation
Index error occurs when the sextant index mirror and horizon glass are not parallel at 0° 00.0'. 'On the arc' errors are subtracted; 'off the arc' errors are added to sextant altitude readings.
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