Wooden instrument used for telling the time at night using the stars of Ursa Major ('Great Bear') and the pole star, Polaris.

For use with Great Bear only, not for both Bears.
Main disc reverse: Circular scale providing the table for the rule of the Pole Star for the Great Bear; numbered clockwise from the top. Within this is the compass rose and a line marking the zeros on the scale. Date scale has named months subdivided to 10 days, 5 days and 1 day. The lunar-age scale is on this disc, within the hour scale.
Rotatabe disc has hour scale only. One shaped pointer with straight edge against the 12 line.