Chinese Tranditional Story: The Legend of Perpetual Calendar

According to the legend, in the Shang Dynasty, although people knew that there were four seasons in a year, but the time of the season is not accurate. A man named Wannian，means Perpetual, wanted to recalculate and to adjust it. So, he thought and thought, then came up with a very good timekeeping method. One day, he was tired from chopping firewood on the mountain, so he sat under a tree to rest. He found that the tree shadow from the sun was moving with time passingby, so he designed a sundial which accurately measured the time of the day. Later, inspired by the Spring Water dripping from the cliff, he made a five-layer clepsydra to calculate the time.