Clock Facts  
The Seven Days of the Week
Astronomical clock from the Abbey of St. Peter, c. around 1750 (Inv. No. 16-0014)
The planets as the names behind the days of the week
Table showing the planetary hours, Nuremberg, 1568 (detail).
The Sequence of the Planetary Symbols: Saturn – Jupiter – Mars – the sun – Venus - Mercury – the moon. The pointer is pointing directly to the sun.
The sequence of the Days of the Week
The Clock of the Abbey of St. Peter Explains Our Days of the Week

Every child knows the sequence of the days of the week, but few people really know why Monday comes after Sunday. The simple wooden-gear clock of the Abbey of St. Peter (Black Forest) can resolve this mystery.
When looking to the starry firmament, we can distinguish the movements of seven celestial bodies.  They are the sun, the moon and five planets, namely Mercury, Venus, Mars, Jupiter, and Saturn. These seven moving stars are behind the names of the  seven days of the week.

The Seven Planetary Symbols
The sequence of the days of the week is not a mystery. Instead, it goes according to a simple pattern, as deciphered on the wooden gear-clock of the abbey of St. Peter. At the lower portion in the middle of the clock there is a dial showing the seven planetary symbols.

They are in the following sequence Saturn – Jupiter – Mars – the sun – Venus - Mercury – the moon.

This sequence corresponds to the speed with which the moving stars travel across the sky. Saturn is the slowest, while the moon is the fastest. But this still does not show the sequence of our days of the week. On the dial, namely, Jupiter (Thursday) is shown to be after Saturn (Saturday).

The sequence of the days of the week
can be seen by letting the clock run: With every hour, the pointer on the clock moves to the next space.
Hence, instead of being able to read the actual day of the week on the dial, we are able to read the corresponding planetary hour ruler. The reasoning behind this is that, in the distant past, it was believed every hour was dominated by a planet.
Over the course of the 24 hours in one day, the pointer thus moves three full cycles (3x7=21), plus it moves ahead another three spaces (21+3=24). This leap across three spaces gives us the correct sequence for the days of the week: Therefore, 24 hours after Saturn (Saturday), the pointer reaches the sun (Sunday), etc.
This is how a simple wooden-gear clock from the Black Forest has preserved the knowledge of bygone days.