How Did the Norse Navigate? in “The Nautical Part”

[…]Captain Carl V. Sølver donated an enormous collection of literature and old instruments to the Museum, amongst these, I found his reconstruction of the bearing-dial and the plastercast of the half-moon shaped wooden disc from Uunartoq.

[…]As Mr. C. L. Vebæk tells us, in 1978 Dr. Curt Roslund came to the National Museum and examined the find. He became convinced that the curve which he had interpreted as a gnomon curve [a curve drawn on the board of a sundial against which the shadow from the gnomon is measured], had been deliberately made visible and his observation changes the interpretation of the find in an almost revolutionary way. The Norse navigator could have used the track of the sun's shadow as a direction finder. […]

Detailed description of the two artifacts from Southern Greenland
The half-moon shaped wooden disc from Uunartoq […] has the following dimensions: From corner to corner it is 70 millimetres, but if it is the half of a circular object, about 2 millimetres should be added. It has a thickness averaging 9 millimetres. The material is spruce or lark. The straight edge has clear signs of having been broken off a larger piece of wood, and it has in the middle a semicircular cut, diameter about 18 millimetres, and this probably was one of the signs leading Captain Carl Sølver to the idea that the wooden disc has been used as a bearing-dial. Here the handle could have been placed.

The most interesting side of the disc, is the one with notches in the round edge, for these certainly led Capt. Sølver to the idea of a bearing-dial. They are marked out in a similar manner to the method by which the early compass was divided — the 32 point division.
The first 10 divisions from the top of the picture, are actually correct within one degree, but the remaining divisions are confusing. Probably the maker had noted the inaccuracy for there are indications that the notch, which I call 13 A may have been erased and, if this is true, then the division is correct within 50, and this is surely tolerable.

Below the upper notch, there are 16 scratches of about 2 millimetres each. If we consider this notch to indicate north, then a deep mark 8 points from there could be east. There are 8 points or 90° in each quadrant of the compass. On the same side as the notches there are also several scratches, but two of them have been traced in to make them more visible. They are in the middle of the disc and led the Sweedish astronomer Dr. Curt Roslund to the idea that they were gnomon curves. The curved line should coincide with the curve for the summer solstice, and the straight line to the equinoxes. Later investigations by the Danish Police Department of Crime have confirmed that the lines had been traced at least twice.

In the lower part of the disc, there are several scratches. They may also be parts of gnomon curves, but this is still uncertain. On the reverse side, there are several scratches, but there is no explanation for these and they are still under consideration. […]

The gnomon curve used as a directionfinder
Gnomon is the Greek word for a vertical pole placed on a horizontal plane. If placed so that the sun can shine on it throughout the day, its shadow will follow the same pattern for a period of days — long in the mornings and afternoons, and shortest at noon, when the shadow in our latitudes will point due north. A bearing-dial or sun compass based on this principle can be made by anyone having a garden or access to another open area in which the sun can shine during the whole day. The illustration shows how to make one and also how to divide it. It is very likely that the Norse navigator made his direction finder this way. With some years' experience, he may have collected patterns suitable for various times of the year. […]