This is a portable cylinder sundial, quite common until the XVIIth century. The instrument is also called "orologio del pastore", since in Europe it was built and used by the shepherds ("pastori") of the Pyrenees up until the beginning if this century.
With the brass gnomon pulled out and placed in line with the date engraved on the cylinder, it was oriented towards the Sun, so that the time could be read on the time lines marked by the shadow.
This sundial shows two gnomons to be used in winter and summer respectively.
A.J. Turner ed. (1990), pp. 70, 105.
G. L'E. Turner (1991), p. 130.