It also details astronomical calculations, calendrical studies, and establishes rules for empirical observation. The system is linked with the Mesoamerican calendrical system, used for divination rituals. The hats are also suggested to have served astronomical/calendrical functions. The Chinese also used the armillary sphere in aiding calendrical computations and calculations. Calendar reform or calendrical reform, is any significant revision of a calendar system. This coincides with an ancient calendrical system divided into twenty-four fifteen-day periods. However, relatively little is known of these ancient calendrical systems. Seven of the calendrical crescents (red) are accompanied by other glyphs (green). Evans never intended to give exact calendrical dates to the pottery periods. The concept was used by several ancient cultures as part of their calendrical system. Other festivals throughout the year are specified by the Balinese "pawukon" calendrical system. Most cases of calendrical calculation involve individuals with IQs that are below average. Classes that store times and dates and represent calendrical information. Most of these ideas were basis for their time-keeping and calendrical activities. Calendrical rites impose a cultural order on nature.