Furthermore, when a measurement did not match a precise
number of «land rods» — their standard unit of linear measurement, which
corresponded to about 2.5 meters — the Aztecs added
symbols, such as an arrow, a heart, a hand, or a bone, to indicate remaining length that was less than one rod.
For processing speed, students were asked to translate
numbers into
corresponding symbols using a
number -
symbol key, and to indicate as quickly as possible under a time constraint whether either of two
symbols on the left side of a page matched any of five
symbols on the right side.