> For the complete documentation index, see [llms.txt](https://docs.ceruleansonar.com/c/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ceruleansonar.com/c/ethernet-rov-locator/configuring-the-rovle/rovle-basic-configuration/magnetic-declination.md).

# Magnetic Declination

<figure><img src="/files/42lrkczg2iqzq4BvH1E9" alt=""><figcaption></figcaption></figure>

The magnetic declination is used if there is no GNSS Compass attached or if the GNSS Compass can't get a good heading fix at the moment.

Magnetic declination (sometimes called magnetic variation) is the angle between magnetic north and true north. Declination is positive when this angle is east of true north and negative when it is west. Magnetic declination changes over time and with location. The declination value is needed to determine true north when using the internal compass and not the GNSS compass, because compasses point toward magnetic north.


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