Enter the date and your DR longitude for the time of local noon. Add the Sun's highest sextant altitude for your latitude.

How a noon sight works

At local apparent noon the Sun crosses your meridian and stands at its highest for the day, due south or due north of you. Its altitude then depends only on your latitude and the Sun's declination, so one sextant reading and the almanac give your latitude. No sight reduction tables are needed, and the time only has to be right to within a few minutes.

The working: correct the sextant altitude to Ho, subtract it from 90° to get the zenith distance, and combine that with the declination. If the zenith distance and declination have the same name (both north, or both south) add them; if contrary, subtract.

The calculator first tells you when noon will be at your longitude, so you know when to be on deck. Enter the altitude afterwards for the latitude.

It is a learning aid, not a navigation tool: at sea, use the official Nautical Almanac and tables, and check every position by other means.

Learn to do it yourself

Latitude from the noon Sun: the whole method, with practice that checks every step.
Sextant corrections: Hs to Ho: index error, dip and the main correction.
Where the Sun is: reading GHA and declination from the almanac.