Click to follow link:
Huarochirí: A Peruvian Culture in Time, by Frank Salomon
Code of the Khipu Databooks, by Marcia Ascher & Robert Ascher
The Harvard Khipu Data Base Project, por Gary Urton
TThe Cord Keepers: Khipus and Cultural Life in a Peruvian Village, by Frank Salomon (Duke University Press, 2004)