The Long Count.
Many early monuments of the Mayas have inscriptions with an enlarged Introducing Glyph containing a variable element indicating the title or principal subject matter of the inscription. Next follows the number of elapsed days from the epoch of a Mundane Era. This starting point is uniformly the day 4 Ahau 8 Cumhu and the complete Initial Series date not only states the number of elapsed days, but also the name and number of the day reached and its position in a Mayan month.
The Initial Series is normally followed by a Supplementary Series which concerns the lunar calendar, and often there are numbers of days to be added to or subtracted from the Initial Series date: these are called Secondary Series. Also Period Ending dates are used, these being merely abbreviated dates which correspond to indicated round numbers in the day count.
The Initial Series analyzed in [Plate XXIII] actually records the number 1,401,217. This number does not, however, reach the day 12 Caban declared immediately after it or the month position 5 Kayab recorded in glyph 10b. When 13 tuns are corrected to 12 tuns on the theory that the sculptor did not follow copy, we do reach 12 Caban 5 Kayab. Another check comes when we add the Secondary Series of 2423 days and reach 4 Ahau 13 Yax ending an even katun.