A homemade mechanical rolling ball clock (english, deutsche Version:    • Murmelbahn-Pendeluhr (DE). Pendulum r...  )
The clock runs for 12 hours, driven by a weight of 2.5 kg sinking approx. 1 meter during that time..Every minute a marble is lifted up and goes down a marble run with three flipping traps that count marbles for minutes, five-minute-steps and hours.
The timekeeping element is a second-pendulum with a pinwheel escapement.

The clock achieves a drift of less than 1 second per day.
I have to admit that this is based on a measurement over 24 hours only, so it does not include large temperature variations. Nonetheless, I did not expect that high accurracy. But keep in mind that a pinwheel escapement is among the most precise.

Stereoscopic photographs of the clock on Google+: http://goo.gl/dWnkb8
Tutorials and plans for my projects: http://turnvater-janosch.blogspot.com/

Material:
Wood (mainly remains)
Plastic gear wheels
Brass wire (1.3mm, 3mm)
Steel wire (bicycle strokes)
Old flat iron