Tlalcuahuitl

Tlalcuahuitl or land rod also known as a cuahuitl was an Aztec unit of measuring distance that was approximately, to or long.
The abbreviation used for tlalcuahuitl is and the unit square of a tlalcuahuitl is.

Acolhua Congruence Arithmetic

Using their knowledge of tlalcuahuitl, Barbara J. Williams of the Department of Geology at the University of Wisconsin and María del Carmen Jorge y Jorge of the Research Institute for Applied Mathematics and FENOMEC Systems at the National Autonomous University of Mexico believe the Aztecs used a special type of arithmetic. This arithmetic the researchers called Acolhua Congruence Arithmetic and it was used to calculate the area of Aztec people's land as demonstrated below: