The numerous types of calendars,  set up  by peoples through the ages, testifies to man's inability to bring into use an  universal calendar accessible to all and simple to use ( see Table II ). In any case, man's touch is omnipresent as if nature presents flaws that would be necessary to correct. 
Indeed, all calendars present themselves as an arithmetic rule that permits the reproducibility of time units defined by  man,  without departing too much from the observation of the concerned stars. This rule also provides for the recuperation of what we call ordinarily  the lost time or the "slip of calendars" - the residue between the observation and the rule - by the simple addition of a time unit at the end of a some period defined beforehand. 
Nowadays, it is the solar calendar that is rife as it secures, in general, a good time conservation  by means of a simple arithmetic rule. It is also the one that experienced the most reforms, going thus from a lunar calendar ( Roman ), to a soli-lunar calendar ( Roman ), then to a merely solar calendar ( Julian ), to finish as a solar calendar ( Gregorian ). 
Unfortunately, this calendar remains very artificial since, besides the year, it is not based on  observable natural facts permitting the knowledge, even for a layman, of the various articulations of this calendar, such as the precise moment of the transition from one day to another, from one month to another, when we know that it is strictly advised against for eyes to linger observing the brightest star of the sky and taking in account that  science must be even in the illiterates' service. How  can we admit that the day begins in a given place when the sun is to the zenith of a diametrically opposite place without having  the visual means to check it. This is in particular that the meridian broken curve of date change has been chosen in deserted regions.   It is the same  for the four types of solar months ( 28, 29, 30 and 31 days ) that are not based on any observable fact. It is not the case for the lunar calendar ( Hegirian ) as the following comparative table shows it.

                               
  Moon phases