Illustrations found in Aztec manuscripts.
An astronomer at work in an observatory. He uses a pair of crossed sticks set up in a window or doorway to determine the position of a star. From the Nuttall Codex.
The same situation in front view. The astronomer's eye is seen between the two crosses sticks. A star is approaching from the right above, and the astronomer waits until it is exactly beyween the crossed sticks. From the Selden Codex.
An arrangement of the two crossed sticks through which the astonomer looks at a V-shaped arrangement in the distance, where the star can be seen. From the Bodleian Codex.
Morley, S. G., G. W. Brainerd and R. J. Sharer (1983) The ancient Maya. Stanford University Press, Stanford, California.