Bifilar Dials

The Doret dial, shown below, is very versatile. It is shown here in horizontal mode but it can be placed on any surface, provided that the hinged style legs point to the pole star. The dial doesn't know where you are on the Earth - it works anywhere, so it is perfectly happy on any wall or other surface anywhere. The only limitation is that the time scale must be clockwise if the legs are pointing up to the north celestial pole, anticlockwise if pointing to the south pole. The illustration shows  both clockwise and anticlockwise hour numbers on it, so is truely universal, like a universal ring dial. Looking for a reference to this dial