The king of all sundials, a Heliochronometer made by John Gunning of Petersfield Hampshire. To quote his website which is full of information and well worth a visit: "It's only the heliochronometer that gives a direct and accurate reading of Standard Time throughout the sunlit year. To a greater or lesser extent, all other sundials fall short of this capability. Most will only reflect accurate time on four days of the year. By comparison, the Heliochronometer is 'right' every day and stands a fair chance of being more accurate than your watch. Clocks and watches, by their very nature, can only keep time whilst sundials determine it. And the unique capability of the Heliochronometer is that it determines it precisely to the minute."