Question 818Navigation General

The correct answer is B) positive correction. When a sextant has an index error that is "off the arc", it means the index correction is positive. This is because the index error is in the direction that increases the altitude measured by the sextant. To correct the observation, a positive correction must be applied to the observed altitude to get the true altitude. The other options are incorrect because: A) Dip error is related to the horizon, not the index error. C) Semidiameter error is a different type of error not related to the index error. D) A negative correction would be applied if the index error was in the opposite direction, decreasing the observed altitude.