Magnetic Compass offline · v1.3

Enter the gyro heading read at each compass heading. Deviation = magnetic heading − compass heading (East +, West −). Everything saves automatically on this device.

Vessel and compass

Position at the time of observation
Latitude
°'
Longitude
°'

Variation, gyro error and limit

Variation at position (degrees)
Gyro compass error (degrees)

True heading = gyro heading + gyro error. Magnetic heading = true heading − variation. East is +, West is −.

Readings

Compass headingGyro headingTrueMagneticDeviationStatus

Correctors on the binnacle (as found)

Pick the number of magnets first, then the slot and the direction of the red end for each one. Use n/a where nothing is fitted. The Adjustment page reads these choices.

Conditions and sign-off

In the print dialog choose "Save as PDF" to keep a copy.

Enter the date, UTC time and position, pick the object from the sky view, then enter the readings you took at the same moment. The app works out the true bearing and the errors.

Observation

Time (UTC)
Latitude
Longitude

Sky view

Readings

Variation

Version 1.3 · built 17 Oct 2026