The Mesoamerican Long Count calendar is a non-repeating base-20 and base-18 calendar used by several pre-Columbian Mesoamerican cultures, most notably the Maya. For this reason, it is often known as the Maya Long Count calendar. Using a modified vigesimal tally, the Long Count calendar identifies a day by counting the number of days passed since a mythical creation date that corresponds to August 11, 3114 BCE in the proleptic Gregorian calendar. The Long Count calendar was widely used on monuments.
Background
The two most widely used calendars in pre-Columbian Mesoamerica were the 260-day Tzolkʼin and the 365-day Haabʼ. The equivalent Aztec calendars are known in Nahuatl as the Tonalpohualli and Xiuhpohualli.
The combination of a Haabʼ and a Tzolkʼin date identifies a day in a combination which does not occur again for 18,980 days (52 Haabʼ cycles of 365 days equals 73 Tzolkʼin cycles of 260 days, approximately 52 years), a period known as the Calendar Round. To identify days over periods longer than this, Mesoamericans used the Long Count calendar.
The Long Count calendar is divided into five distinct units:
- one day - kin
- 20 days - uinal
- 360 days - tun
- 7,200 days - katun
- 144,000 days - baktun
Mesoamerican numerals
Long Count dates are written with Mesoamerican numerals, as shown on this table. A dot represents 1 while a bar equals 5. The shell glyph was used to represent the zero concept. The Long Count calendar required the use of zero as a place-holder and presents one of the earliest uses of the zero concept in history.
The Mesoamerican Calendar - Ancient Americas 
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This is so fun and cool, the only bus that takes me home is supposed to come every 20 minutes, but they like to get so off schedule that currently the two busses on that route are currently one behind the other, with 40 minutes between them both showing up at the same time.
I fucking hate this city.
see, what they do here when that happens is they just tell the second bus to chill at the bus station for ages, without warning anyone on the route that their bus isn't coming lol
I was gonna say this sounds like my bus rn, but then I realized that that it sounds like every bus I've ever taken to work. Public transit is such a joke rn :(