December 21 2012 End date of the Mayan Long Count Calendar may be off by at least 60 days
According to an online Discovery News article by Ian MacNeill, the Mayan end of the world 2012 date might be off by at least 60 days.
The problem has to do with correlating dates in the Mayan Long Count calendar with dates in our present Gregorian calendar. Scholars use a constant called the GMT constant, which refers to the initials of the three men who determined this constant: Joseph Goodman, Juan Martinez-Hernandez and J. Eric S. Thompson.
Carol Chapman, author of the End of the World 2012 EBook