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Full-View sextant Though this may be a trade name for one specific model, it generally refers to that type of sextant horizon mirror with a special horizon glass that replaces the traditional split mirror with an optically coated glass that both reflects and transmits light over the full range of view. It makes easy sights easier, but hard sights harder, since its principle of operation loses light intensity at the horizon glass. Nevertheless, they are attractive to first time sextant users because most sights fall into the easy category. Problems occur for faint stars, or when checking the index correction and inverting the sextant when there is little contrast between sky and water color. Daylight moon sights are nearly impossible when moon is newish and sky is light blue. Full-view mirrors are also difficult to use for sextant piloting. See Index Correction, Inverting the Sextant, and Horizon Mirror, Sextant Piloting. It is interesting to note that this mirror technique was invented by Davis Instruments, makers of plastic sextants, though this option is now available on most metal sextants. It was more popular when it first came out than it is now, as mariners learn of its limits.

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