Work your own sight

Took a real sight? Enter it here and the app reduces it the way the course teaches, showing every number, so you can check your own work. Add two or three lines to plot a fix.

For learning, not for navigating. This is a teaching tool. Do not rely on it for the safety of a vessel: navigate with the official Nautical Almanac and tables, and check every position by other means.

Work the sight by

Pub. 249 Pub. 229 Formula (calculator)

Body

Date (by your watch)

The almanac covers 2026 to 2028.

Watch time of the sight

hours, minutes and seconds, like 2 31 00

Zone description (hours)

UT = zone time + ZD. 0 if the watch keeps UT.

Watch error (seconds)

+ if the watch is fast, − if it is slow.

Horizon

The sea horizon, from a boat or the shore.

Sextant altitude, Hs

degrees and minutes, like 51 35.6

Index error (minutes)

“On the arc, take it off.”

Height of eye

Above the sea, where you stood.

DR latitude

like 22 17.9, then N or S

DR longitude

like 140 05.2, then E or W