separació dels grups de tres dígits 

Matemàtiques

Pel que fa a la separació de grups de tres dígits, cal tenir en compte el que es diu en els documents següents:

En la publicació del NIST Guide for the Use of the International System of Units (SI), dins l’apartat 10.5.3, «Grouping digits», es diu el següent:

«Because the comma is widely used as the decimal marker outside the United States, it should not be used to separate digits into groups of three. Instead, digits should be separated into groups of three, counting from the decimal marker towards the left and right, by the use of a thin, fixed space. However, this practice is not usually followed for numbers having only four digits on either side of the decimal marker except when uniformity in a table is desired.»

En aquest text, doncs, es considera que l’espai fi es pot posar també en els nombres de 4 dígits si aquests estan encolumnats amb altres nombres de més dígits per tal que la presentació sigui uniforme.

El mateix es diu a The International System of Units (SI), 8a edició, 2006, dins l’apartat 5.3.4, «Formatting numbers, and the decimal marker»:

«The symbol used to separate the integral part of a number from its decimal part is called the decimal marker. Following the 22nd CGPM (2003, Resolution 10), the decimal marker “shall be either the point on the line or the comma on the line.” The decimal marker chosen should be that which is customary in the context concerned.
»If the number is between +1 and −1, then the decimal marker is always preceded by a zero.
»Following the 9th CGPM (1948, Resolution 7) and the 22nd CGPM (2003, Resolution 10), for numbers with many digits the digits may be divided into groups of three by a thin space, in order to facilitate reading. Neither dots nor commas are inserted in the spaces between groups of three. However, when there are only four digits before or after the decimal marker, it is customary not to use a space to isolate a single digit. The practice of grouping digits in this way is a matter of choice; it is not always followed in certain specialized applications such as engineering drawings, financial statements, and scripts to be read by a computer.

»For numbers in a table, the format used should not vary within one column.»

Finalment, cal tenir en compte també que, d’acord amb la norma ISO, es recomana l’ús de l’espai fi com a separador i es desaconsella l’ús d’altres separadors (com ara el punt o la coma):

«To facilitate the reading of numbers with many digits, these may be separated into suitable groups, preferably of three, counting from the decimal sign towards the left and the right; the groups should be separated by a small space, and never by a comma or a point, nor by any other means (ISO standard 31-0).»

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