• 4: I'm curious, do you have a link to the video? I don't see a reason that you 'need' the compass app. But as a casual sailor I say a compass generally often helps.
    In the button menu of the osm app you can switch the direction marker between GPS and compass, you can also reset the compass here for recalibration. That should cover most requirements of the compass app.

    6: Mainly position + direction. It is also commonly used by the recorder app when plotting the course.

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