Note that the units of the LC reflect the base 20 (vigesimal) mathematics common to ancient Mesoamerica. In the LC, though, the 3^rd-place unit of the system is 360 rather than the expected 400. All of the higher units are proper vigesimal multiples of 20 (a k’atun of 7200 days is 20 tuns of 360 days, etc.).

This departure from a purely vigesimal system may have been motivated by the ancient Maya interest in how their multiple calendar cycles worked together. 360 is evenly divisible by 9, so that the same “Lord of the Night” (Glyph G series) was in the ascendant at the beginning of every tun and of every larger period.

An LC date can be treated as a 5-digit number, keeping in mind the deviation of the 3^rd place. In doing LC arithmetic (to work out Distance Numbers, for example) note that the number of uinal cannot be greater than 17.

1 1 1

9 . 0. 19. 17. 19

+ 1

_________________

9 . 1. 0. 0. 0

1 day added to 19 k’in makes a full winal, so the k’in digit becomes 0 and 1 is carried to the winal place. 1 winal added to 17 winal makes one full tun, so the winals digit becomes 0 and 1 is carried to the tun place. 1 tun added to 19 tun makes a full k’atun, so the tun digit becomes 0, 1 is carried to the k’atun place, and the k’atun digit becomes 1.

There is a very good web calendar calculator on the FAMSI website. See the section below.

Of the many Maya local calendar calculators available, Mayadate has the greatest number of features. It is a PC program, but runs fine under Mac PC emulators. It can be downloaded from the Mayadate home page.