The Mayan numerical system was vigesimal (20-base); symbols were given a value according to position and the concept of zero was known. Three symbols were used in writing numbers: a dot for one, a bar for five and a seashell for zero. This was the most common way of expressing mathematical computations.
Another mathematical system, more intricate and complex, was also employed. This one utilized glyphs representing assorted deities.
Fig. 1-1. One way of writing Mayan numbers. Each number from 1 to 12 is represented by the head of a different deity, while the glyphs for 13 through 19 are composites formed by adding part of the sign for 10 (the fleshless jaw of a skull) on the heads for 3 to 9. Some, but not all Mayan languages form the words for these numbers in just this way, with unique words for "eleven" and "twelve" but with "three" through "nineteen" combining the elements for the words "three" through "nine" with that for "ten."
Fig. 1-2. Maya numbers. The commonest method of writing numbers features a dot for 1 and a bar for 5. For numbers greater than 19, Maya place-notation employs a stylized sign (a shell in the painted books) for 0. The place system is vigesimal, so that the value of the places increases by 20 (reading up). For time calculation, however, a special convention sets the third place equal to 360 instead of 400.