A means of recording time in the Mesoamerican Preclassic period, the only one to refer to an initial fixed date, which was perhaps the equivalent of 3113 BC. Passage of time recorded in decreasing units equaling x times 144,000 days (day is 'kin'), x times 72,000 days, x times 360 days, x times 20 days, and x times 1 day. In Maya lowlands in south, the Long Count system was used between c 300-900 AD but Mayas are not thought to have invented this system of calculation. The units of measure are kin, uinal, tun, katun, and baktun - mainly progressing by 20s.