The four figures at the top, in the medieval times were seen as the four menacing elements for the city of Prague.These have moving parts although they themselves remain where they stand all the time.The second gears the indicator of the Sun and rotates once a mean solar day.
Further developments in clockwork mechanisms made it necessary or viable to be able to divide time into units.
The Orloj, also known as The Prague Astronomical Clock is one of the oldest European clocks of its kind (the first ever originated in Padua in 1344 and a second in Strasbourg in 1354) and continues to hold its exceptional position.
The ball, half silvered and half black, rotates every synodic month and displays its phase.
The Calendar is the bottom part of the Orloj with month symbols painted by Josef Manes in 1805.
In times when clock works were imprecise in maintaining their continuous precision, it was necessary to keep correcting them, comparing clocks with other clocks and the best way to do this was according to the then sun clock measurements - the sun dials.