Andy,
Yes their calendar was that accurate. I did not know it was that accurate until I seen it on Science or PBS program a few weeks ago....They said that's why they did not use a Leap Year. Modern man made leap year so we could make each day 24 hours long and account for the little bit of extra time every for years when it equaled a full day. Even now they still make adjustments of a second or two on some New Years to correct for those few seconds of inaccuracy not corrected by adding a day in Leap Years.
I think their long count calendar runs for about 5193 years which is supposed to be when the planets and the Sun again align with the center of the Galaxy. The other 2 calendars were short count calendars I think one lasted 53 days, and the other was about 56 years??.
The Mayan's made long count calendars that went back over 20,000 years BC Each time the Long count calendar ran out, they believed the earth was sort of reborn??? The Mayan's made a total of 5 long count calendars and the 5th one ends on Dec 21st 2012, so the speculation is that marks the end of the world...Some people think that because the calendars went back for over 20,000 years that they would have continued their calendar farther into the future with a 6th or 7th long count calendar. By stopping at the end of the 5th calendar, some people assume that is predicting the end of the world.
Scientist say that when the sun and all the planets align with the center of the Galaxy, there will be additional gravitational forces pulling on the earth. This could cause some higher tides, and perhaps even trigger some earthquakes, but most do not think it will be anything as dramatic as some people think? But who knows...???
...Rich