Winner of the 2005 Kokuyo design awards, this calendar uses weight to determine what month it is. From robotic translation we can gather that you place the weight on the spring, and depending on how heavy the current date is, "the machine which measures the time" is. Yeah.
However it works, it's much better than our method of carving a tick into the wall for each passing day. Our landlord disapproves.
Kokuyo Prize 2005 [Kokuyo]