An obvious disadvantage of the lunisolar method of inserting a whole extra month is the large irregularity of the length of the year from one to the next. The simplicity of a lunar calendar has always been outweighed by its inability to track the seasons, and a solar calendar is used in conjunction to remedy this defect. Identifying the lunar cycle month requires straightforward observation of the Moon on a clear night. However, identifying seasonal cycles requires much more methodical observation of stars or a device to track solar day-to-day progression, such as that established at places like Stonehenge. After centuries of empirical observations, the theoretical aspects of calendar construction could become more refined, enabling predictions that identified the need for reform.