Apart from a portable watch, this device was also a diary of the early Byzantine era.
It has a disk shape with a diameter of 13.5 cm and a depth of 1.5 cm.
It bears the names of the months of the Julian Calendar which are the same as today as the symbols of the days of the week. The names of the main cities of the known world of the time are also listed in Greek, as well as their latitude in degrees.
It is made of brass and dates back to the 5th or 6th century AD.
At that time there were other portable watches but this is distinguished because it has a system of shafts and gears to show the phase of the Moon, the day of the month and the position of the Sun.
It is the second oldest gear mechanism discovered after the Antikythera Mechanism.
Today it is on display at the Science Museum in London.
[Source: el.wikipedia.org]
