Although we agree that micro-controllers and RTCs are fun, it is really intriguing to look at a completely mechanical clock. A Pendulum Marble Clock (German Version) was designed by Turnvater Janosch. It is said that it runs for 12 hours at a time using gravity and also has the accuracy error which is less than 1 second per day.
It works by lifting a weight of 2.5 kg which descends around one meter during that time of twelve hours. There is a series of steel ball bearing to count the minutes, 5 minute increments and hours.
One ball is released on the track for each minute and when the track fills up, trap doors will open to release the ball to the next level. The next level being 5 minutes. It goes like this: First level: minutes, second level: 5 minutes, third level: hours.
The whole thing is made out of wood, brass and steel wire, plastic gears and an old flat iron. However, there’s no accurate info on why the iron is actually used.