While the absence of ceramics appears anomalous, the presence of textiles is intriguing. "Quipu" (or khipu), string-based recording devices, have been found at Caral, suggesting a writing, or "proto-writing", system at Norte Chico. (The discovery was reported by Mann in "Science" in 2005, but has not been formally published or described by Shady.) The exact use of quipu in this and later Andean cultures has been widely debated. Originally it was believed to be simply a mnemonic used to record numeric information, such as a count of items bought and sold. Evidence has emerged that the quipu may also have recorded logographic information in the same way writing does. Research has focused on the much larger sample of a few hundred quipu dating to Inca times; the Norte Chico discovery remains singular and undeciphered.