a "yard" for measuring something; or, a sampler, an example of something for a demonstration (see Molina)
Alonso de Molina:
tlaoctaca anoni. vara para medir algo, o dechado de donde sacan labor, o muestra &c. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 129v. col. 2. Thanks to Joe Campbell for providing the transcription.