The peoples living in the east called the doeru an almanac for calculating time. At present, this word is not used and has been replaced by the word calendar. This measure previously corresponded almost exclusively to one revolution of the moon. Naturally, the moon, with its regular phases, could not but become a measure for calculating time. Something of the original lunar calendar remains in our way of dividing time, this is the month. the number of days of which approximately corresponds to the duration of one revolution of the moon. But the moon is not the beginning governing our day and seasons. It is not the moon that governs the sowing, reaping and harvesting of grapes. Therefore, the convenience of a calendar based on the apparent annual movement of the sun has long been recognized. The Egyptians, apparently, were the first people to whom this happy thought was born. But the lack of astronomical knowledge forced them to take constant new value in 365 days. It is now known that it takes 365 days, 5 hours, 48 minutes and 48 seconds for the earth to travel the entire path of its annual orbit. Thus, the year of the Egyptians differed from the actual one by almost one quarter of a day. This error gradually grew, reaching the size of a day, even whole weeks, which, of course, brought with it great inconvenience.