Ancient egyptian dating system
(This division of the night sky, later adjusted to account for the epagomenal days, had close parallels to the Babylonian zodiac.
The signs of the zodiac each accounting for three of the decans.
An improved version using a rod (or gnomon) and which indicates the time according to the length and position of the shadow has survived from the second millennia BCE.
Problems with observing the sun and stars may have been the reason the Egyptians invented the water clock, or "clepsydra" (meaning water thief in Greek).
The months of the Egyptian civil calendar were further divided into three sections called "decades", each of 10 days.
(This is most unusual since other civilizations of that era are known to have started months with the first setting of the new crescent!
) A thirteenth month was intercalated to maintain a link to the heliacal rising of Serpet. The second calendar, used for administrative purposes, was based on the observation that there was usually 365 days between the heliacal rising of Serpet.
Marks on either container can be used to give a record of hours passed.
Some Egyptian clepsydras have several sets of marks to be used at different times of the year, to maintain consistency with the seasonal temporal hours.This pre-dates the Julian reform of 46 BCE which Julius Caesar introduced on the advice of the Alexandrian astronomer Sosigenese.