Question 815Navigation General

The correct answer is C) negative correction. When a sextant has an index error that is "on the arc", it means the index correction is negative. This is because the sextant is reading a higher angle than the true angle being measured. To correct for this, a negative correction must be applied to the sextant reading to obtain the true angle. The other answer choices are incorrect because: A) A positive correction would be used if the sextant was reading a lower angle than the true angle. B) Dip error is a separate type of error caused by the observer's height above the horizon. D) Semidiameter error is a different type of error caused by the size of the observed celestial body.