definition
strict definition
sundial
A calibrated device on the facade of a structure which displays the time using shadows cast by the sun.
A sundial is a device which tells the time by casting a shadow according to the sun's position. It is listed as a public amenity for a structure when it is permanently displayed on the facade or outer surface.
The position of the cast shadow provides the time indication. The device must be a permanent feature of the facade or another outer surface of the structure.
An ordinary shadow on a wall does not itself make the surface a sundial; the device is arranged to indicate time. Exterior clocks provide a separate digital or analog timepiece display.