Digital sundials

The digital sundial is a fairly recent invention. The time is displayed in digits or even in words or pictures. This sort of dial is not easy to built and works as follows:

"Two closely-spaced parallel masks project different images depending on the angular position of the sun in the following way: The first mask casts a striped light pattern which is dependent on the height of the sun onto the second mask The second mask is composed of narrow stripes of the digits to be displayed.
The striped pattern of sunlight cast by the first mask illuminates exactly those stripes of the second mask corresponding to the image representing the current time." (Scharstein, 1996.)

For more information about his type of dial visit their web site at:
www.digitalsundial.com