The Vikings used the same geometrical method constructing both Trelleborg and the bearing-dial.
Click image at left:
1. Draw declination (blue lines)
2. Draw points of compass (green lines)
3. Draw eykt (time, red lines)
4. Draw scale of latitude (stipled lines)
The method used by the Vikings when constructing Trelleborg (one of many danish Viking Strongholds) around 980 AD, showing that this is a common constructing method for the Vikings in Scandinavia. (This note to express that the Vikings had a geometrical approach finding declination and summersolstice at a given latitude, not analytical but geometrical - click here for more information about Trelleborg construction).
Make your own experiments with Viking geometry and the bearing-dial here.