I have a sundial in my back garden. A really unique face on it, picked it up in Quebec City a few years back. Works quite well (roughly within the hour) if it is pointed in the correct direction. Jim Dixon's post explains the setup and how they work. Don't know much about grandfather clocks, but I do have a cuckoo clock and it doesn't work well. But that doesn't really matter since it is a 'cuckoo' clock.

sIx