Excellent find, thanks! Funnily enough I was at the Guild Hall yesterday during my lunch hour as I work about 30 seconds walk away from it. There is a small museum in it which is sponsored by the Guild of Clock makers. Some great stuff there, like a 'wrist watch' which was a small sundial mounted on top of a compass, and John Harrison's No. V (of the Longtitude by Dava Sobel fame). There is also a great public library which I am going to start exploring for medieval / cartography stuff.