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Apparent Height Every sight reduction starts with the sextant height (Hs) and ends up with the observed height (Ho). But to get there we must first figure this intermediate value, called the apparent height (Ha), which has only the index and dip corrections removed: Ha = Hs + IC - Dip. This height should be agreed upon by all observers who took sights at the same time, even though they used different sextants (different ICs) and stood at different elevations (different dips). It is only "apparent," however, because it is not corrected yet for refraction and semidiameter. An apparent height can apply to the lower or upper limb of the sun or moon. Abbreviation:  Ha

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