Show Magnetic Variance on instrument - Printable Version

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Show Magnetic Variance on instrument - SkipperEarly - 2020-03-07

My objective is to display the magn.variance on a remote display (e.g mobile phone with KIP instrument in browser).
OpenCPN WMM plugin shows the variance but how does it get sent to SignalK so that the navigation.magneticVariance key is set based on the current location.

My understanding is that variance is transmitted a part of the RMC sentence.
I am using moitessier hat and notice that the RMC sentence shows always 0 in the variance position.
Having tested another GPS I see the same behavior.

How can I add the value from the WMM to this RMC sentence ?
- or is there another solution to add the correct - location dependent value for the navigation.magneticVariation key ?