Hello,
I failed to see that in the following question, the gyro north was at 0° initially ! I thought the gyro north was at the real north initially (how stupid am I?)
https://i.gyazo.com/6c17d40997881b47...31be630be9.png
So I started to make a huge fuss about this, including a polar navigation sketch in Google Earth.
Let's not loose it, as it took a bit of time to make :
https://i.gyazo.com/ce5e898881efc970...187450823b.jpg
If anyone would like my explanation as to how the picture is made and what the reasoning behind it is, do not hesitate to ask further clarification.