“Trace of time” is a different type of wall clock designed by Il-Gu-Cha. Its really a day-planner which you can use on daily basis, to visualize your day’s activities while pacing them with the corresponding time. The writeable glass surface works like a board and all appointments are written by you and wiped away by the rotating hand as it passes over.
Source: Pourya’s Blog » Blog Archive » Write your own clock

All very well but how much is it for something you could manufacture yourself with inexpensive components?