[cornholio]

Im still unclear how they determined the constant to convert from long mesoamerican to GMT. What common reference event could allow syncing these calendars to a +/- 3 day precision? I would guess some solar eclipse pattern visible from both sides of the Atlantic?

[apothegm]

They knew about and could identify solstices, which gives you day of the year. So then it’s just a matter of matching years, which can be done on the basis of things like comets.

Supernovae could also play a factor. Or using tree rings to identify years mentioned as having droughts or floods.

Probably a bunch of other things we haven’t thought of.

[gucci-on-fleek]

The Wikipedia page linked in the article [0] has a plausible-sounding explanation.

[0]: https://en.wikipedia.org/wiki/Mesoamerican_Long_Count_calend...

[nraynaud]

I guess in modern time we can compute eclipses from the past?