Accurate Calenders for You
As accurate as calenders get, the western calenders is not fully accurate. This is why every four years there is a leap year. There are also other things to notice that there are slight discrepancies in the calenders at several points in the year. The most accurate calenders is said to be the Mayan calandar or lunar calendar. This calendar is based on the moon and other astrological things. An accurate calenders would have to take into account several things and even then may not be precisely accurate. The earth has 4 seasons that are not exactly equal all the time. The calendar cannot always be exact.
calenders Seasons
Calenders can divide the season up into several months. There are four season and twelve calandar months. The months are not normally equal in length. The season is, therefore, three calenders months long. If there is a problem with the math then please use the correct math and ignore the above said, mathematically. Calenders can be a great way to keep track of time and schedule things ahead of time. This is why calandars were invented. Every since the invention of the calenders was invented things could be accurately scheduled far in advance and things, such as birth days and age could be kept track of.
Invention of the Calendar
There is no real way to tell who invented the calendar, only approximations as we don't know everything about history. The calandar can be traced back many many years to several different societies. It is accurate to say that the calendar was invented somewhere first because it is unlikely that two or more people invented the calandar at the same time. The concept of the calendar may have been around for a while, but it takes a bit of thinking to actually invent the calandar.