**Temporal hours**

This shadow clock is a replica of an Egyptian sundial from the time of Seti I (1290 to 1279 BC). The description of this sundial was found in the Osireion - a temple dedicated to the god Osiris near the tomb of Seti I.

This clock was about dividing the time from sunrise to sunset. The crossbar (shadow caster, gnomon) was placed in the east in the morning. After that, the shadow on the longitudinal beam moved from west to east - in the picture from left to right. According to our time measurement today, the shadow in the image indicates approximately 9:15 a.m. When the shadow no longer fell on the yardstick, the midday break (Ahat) ordered for agriculture began and the clock was rotated 180° to measure afternoon time.

This type of time measurement results in the "temporal hours" (see next page), which were only replaced by hours of the same length with precise gear clocks.

In this way the length of the day (of brightness) is measured and divided, although the Egyptians knew that the temporal length of the divisions depended on the season, but in agriculture at that time one could only work during daylight (diurnal work). The term 'hour' itself was first coined by the Romans (hora).

The division into 12 hours results from the way you counted with your fingers (see picture).

In Saarbrücken, the hours would vary between 40 minutes in winter and 80 minutes in summer. At 12 night hours it is the other way around.

From the way you count, there are many number systems:

- Since we count with our fingers (including thumbs), the decimal system has prevailed with us.

- The Babylonians used a sixty system. They had 59 digits in cuneiform. They didn't know the zero.

- The Romans did not use a place value system.

- Since the toes were also used when counting in France, they had a system of twenty, e.g. B. quatre-vingt for 80.

- Computers calculate with bits (dual system).

- 8 bits are combined into one byte. A byte can store 16 digits, which results in the hexadecimal system with the digits from 0 to F.