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The universal sign for the number 1 in different Mesoamerican writing systems was a dot. In the written texts of the sixteenth-century Mexican highlands, larger numbers were represented by rows of dots, sometimes linked by lines (Chapter 13). In the Maya manuscripts created in Yucatan at the same time, in contrast, a separate sign stood for the number 5. Represented as a solid bar, the same sign can be recognized in inscriptions on earlier Classic Maya monuments. It also appears in monuments from Classic and Late Formative Oaxaca (Chapter 8). In some examples, the bar is drawn as a thumb, suggesting it stood originally for five fingers.

Using these two symbols, numbers could be expressed through combinations of dots (standing for one digit) and bars (standing for five). One dot (1), two dots (2), three dots (3), four dots (4), one bar (5); bar and dot (6), bar and two dots (7), bar and three dots (8), bar and four dots (9); two bars (10), two bars and dot (11) two bars and two dots (12); and so on went the mathematical notation used by Postclassic Maya until after three bars and four dots (19) it reached a full set of 20, the base of the Mesoamerican mathematical system.

Rather than expressing 20 as a set of four bars, the Maya developed the use of place notation, including a third mathematical symbol that could serve as a placeholder, like the zero of Arabic math. This third symbol allowed Mesoamerican mathematicians to record multiplace numbers. Because the base of the Mesoamerican number system was 20 (rather than the familiar base 10 of European decimal mathematics), each place in Mesoamerican math recorded multiples of 20:20, 400 (20 × 20), 8,000 (20 × 20 × 20), and so on.

Sixteenth-century manuscripts recording the tribute paid to the Mexica empire used the expected units of measurement of 20, 400, and 8,000. In addition to this pure use of base 20 mathematics for counting economic goods, however, by the sixteenth century, Mesoamerican people had modified it to allow them to count long periods of time using three signs (one, five, and zero) and place notation.