From earliest times the Babylonian calendar consisted of 360 days. As time went on it was realized that this was not an accurate calendar, so days occasionally were added to it. The length of the year was measured by the number of days it took the earth to make one complete revolution around the sun. In order to carry out the calculations necessary in astronomy, the Babylonians made use of numeration system far superior to that found in Egypt. In fact, we can find many traces of the Babylonian system in our modern culture. It was system based partly on grouping by tens; but as the value of numbers increases, a system of grouping by sixties also came into use.