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A wristwatch sundial (EP 1026558) has been invented by Richard Keatch of
Aberdeen. At its heart is a light-tight box that has a network of tunnels
running from one wall to another. The tunnels are angled at 15 degrees to each
other and terminate in holographic plates which display a time digit when
illuminated. At any given time of day, light passes down only one tunnel,
depending on the position of the Sun. When the wearer uses the wristwatch’s
built-in compass to point south, the displayed digits tell the time.