Shadow analysis….LOL
From an interesting article on sundials on Wikipedia:
The earliest household clocks known, from the archaeological finds, are the shadow clocks (1500 BCE) in ancient Babylonian astronomy. Ancient analemmatic sundials of the same era (about 1500 BCE) and their prototype have been discovered on the territory of modern Russia.
Designers of the Taipei 101, the first record-setting skyscraper of the 21st century, brought the ancient tradition forward. The tower, tallest in the world when it opened in Taiwan in 2004, stands over half a kilometer in height. The design of an adjoining park uses the tower as the style for a huge horizontal sundial.