Editing Abacus (section)

===Native America===
[[File:Quipu.png|thumb|Representation of an [[Inca]] [[quipu]]]]
[[File:Yupana 1.png|thumb|A [[yupana]] as used by the Incas]]
Some sources mention the use of an abacus called a ''nepohualtzintzin'' in ancient [[Aztec]] culture.<ref>{{harvnb|Sanyal|2008}}</ref> This [[Mesoamerica]]n abacus used a 5-digit base-20 system.<ref>{{harvnb|Anon|2004}}</ref> The word Nepōhualtzintzin {{IPA|nah|nepoːwaɬˈt͡sint͡sin}} comes from [[Nahuatl]], formed by the roots; ''Ne'' – personal -; ''pōhual'' or ''pōhualli'' {{IPA|nah|ˈpoːwalːi}} – the account -; and ''tzintzin'' {{IPA|nah|ˈt͡sint͡sin}} – small similar elements. Its complete meaning was taken as: counting with small similar elements. Its use was taught in the [[Calmecac]] to the ''temalpouhqueh'' {{IPA|nah|temaɬˈpoʍkeʔ}}, who were students dedicated to taking the accounts of skies, from childhood.

The Nepōhualtzintzin was divided into two main parts separated by a bar or intermediate cord. In the left part were four beads. Beads in the first row have unitary values (1, 2, 3, and 4), and on the right side,  three beads had values of 5, 10, and 15, respectively. In order to know the value of the respective beads of the upper rows, it is enough to multiply by 20 (by each row), the value of the corresponding count in the first row.

The device featured 13 rows with 7 beads, 91 in total. This was a basic number for this culture. It had a close relation to natural phenomena, the underworld, and the cycles of the heavens. One Nepōhualtzintzin (91) represented the number of days that a season of the year lasts, two Nepōhualtzitzin (182) is the number of days of the corn's cycle, from its sowing to its harvest, three Nepōhualtzintzin (273) is the number of days of a baby's gestation, and four Nepōhualtzintzin (364) completed a cycle and approximated one year. When translated into modern computer arithmetic, the Nepōhualtzintzin amounted to the rank from 10 to 18 in [[floating point]], which precisely calculated large and small amounts, although round off was not allowed.

The rediscovery of the Nepōhualtzintzin was due to the Mexican engineer David Esparza Hidalgo,<ref>{{harvnb|Hidalgo|1977|p=94}}</ref> who in his travels throughout Mexico found diverse engravings and paintings of this instrument and reconstructed several of them in gold, jade, encrustations of shell, etc.<ref>{{harvnb|Hidalgo|1977|pp=94–101}}</ref> Very old Nepōhualtzintzin are attributed to the [[Olmec]] culture, and some bracelets of [[Maya peoples|Maya]]n origin, as well as a diversity of forms and materials in other cultures.

Sanchez wrote in ''Arithmetic in Maya'' that another base 5, base 4 abacus had been found in the [[Yucatán Peninsula]] that also computed calendar data. This was a finger abacus, on one hand, 0, 1, 2, 3, and 4 were used; and on the other hand 0, 1, 2, and 3 were used. Note the use of zero at the beginning and end of the two cycles.

The [[quipu]] of the [[Inca]]s was a system of colored knotted cords used to record numerical data,<ref>{{harvnb|Albree|2000|p=42}}</ref> like advanced [[tally stick]]s – but not used to perform calculations. Calculations were carried out using a [[yupana]] ([[Quechua languages|Quechua]] for "counting tool"; see figure) which was still in use after the conquest of Peru. The working principle of a yupana is unknown, but in 2001 Italian mathematician De Pasquale proposed an explanation. By comparing the form of several yupanas, researchers found that calculations were based using the [[Fibonacci sequence]] 1, 1, 2, 3, 5 and powers of 10, 20, and 40 as place values for the different fields in the instrument. Using the Fibonacci sequence would keep the number of grains within any one field at a minimum.<ref>{{harvnb|Aimi|De Pasquale|2005}}</ref>