3D Reconstruction of the compass dial artifact as a combination of a sun-compass and a sun shadow board. The gnomonic lines belong to a low rectangular gnomon and serve to identify the noon period. The series of 17 notches in the north form a fine scale for reading the noon shadow length of a second high central gnomon with a height chosen for the given latitude and time of year. Deviation from the desired latitude can be read with a resolution of about 0.1° at noon, but only crude bearings can be taken from the compass at intermediate solar elevation angles when this compass is floating in a bucket of water.
Credit: Balázs Bernáth, et al. ©2013 Royal Society Publishing