Calendar family
Astronomical
Time read from the sky: unbroken day counts, star time, and the interlocking rounds of Mesoamerica.
5 reckonings
Aztec (Mexica)
Xiuhpōhualli & Tōnalpōhualli · the Caso correlation
Julian Day Number
Astronomers' continuous day count · itself a running clock
Maya Calendar Round
Tzolk'in × Haab' · repeats every 52 years
Maya Long Count
Mesoamerican · GMT correlation
Sidereal Time
Greenwich Mean Sidereal Time · itself a running clock