Moon Dials

[PsykoKidd]

       I'm a little confused about what practical use a moon dial would have, since the moon is much more transient than the sun.  A superior nocturnal dial would be one that user would line up some of the circumpolar constellations/stars after setting the month and date.  Of course you'd need moon light to read it, unless you install indiglow.
      Anyway, I'm curious how in principle does it work?