Hour system on horizontal dial
The dial is described in Gouk, Ivory Sundials of Nuremberg, p. 124 as having 'a series of nine concentric circles for Italian hours 0-16 throughout the year, but with no scale to indicate the relevant month'.
However the hours are not Italian. They could be either Babylonian or, more likely, Nuremberg. The scale to use is indicated not by month but by length of the day (shown at the sunset end of each scale), in conjunction with the vertical pin gnomon indicating the length of the day.