A method employed by the Maya of measuring the passage of time, comprised of two separate calendar systems: the Calendar Round, used for everyday purposes, and the Long Count, used for the reckoning of historical dates. Maya chronology consisted of three main elements: a 260-day sacred year (tzolkin) formed by the combination of 13 numbers (1 to 13) and 20 day names; a solar year (haab), divided into 18 months of 20 days numbered from 0 to 19, followed by a five-day unlucky period (Uayeb); and a series of cycles - uinal (20 kins, or days), tun (360 days), katun (7,200 days), baktun (144,000 days), with the highest cycle being the alautun of 23,040,000,000 days. All Middle American civilizations used the two first counts, which permitted officials accurately to determine a date within a period defined as the least common multiple of 260 and 365: 18,980 days, or 52 years. The Classic Maya Long Count inscriptions enumerate the cycles that have elapsed since a zero date in 3114 BC. Thus, 9.6.0.0.0 a katun-ending date, means that nine baktuns and six katuns have elapsed from the zero date to the day 2 Ahau 13 Tzec (May 9, AD 751). To those Initial Series were added the Supplementary Series (information about the lunar month) and the Secondary Series, a calendar-correction formula that brought the conventional date in harmony with the true position of the day in the solar year.