ISO 31-0

ISO 31-0 is the introductory part of the ISO standard ISO 31 of the International Organization for Standardization ( ISO) to physical quantities and units. Under the heading General principles ( principles), to be submitted (in particular the International System of Units ( SI) ) Guidelines for the use of physical quantities, symbols for quantities and units as well as single unit systems. ISO 31-0 is intended for use in all areas of science and technology and is extended by specialized conventions that are defined in other sections of ISO 31.

Scope

ISO 31 deals exclusively with physical parameters for the quantitative description of physical phenomena, reference value scales ( such as the Beaufort scale, the Richter scale or color saturation scales), currencies or information contents are not treated.

Quantities and units

Physical quantities can be divided into common categories with each other. For example, drop length, width, height, diameter and wavelength in the same category because they are all the same type sizes ( quantities of the same kind). A specific example of such a size can be used as a reference. Using this so-called unit ( unit) can then all sizes the same category are expressed relative to this unit, in which she with a number - (also called metric ) the so-called numerical value - are multiplied.

If we write, for example, that the wavelength λ = 6.982 × 10-7 m, then λ (lambda ) is the symbol for the physical size of the wavelength, m is the symbol for the unit (meters) and 6.982 × 10-7, the numerical value of the wavelength in meters. In general: A = { A} · [ A] is expressed by A as a symbol for the size, { A} as a symbol of the value and [A] as a symbol for the corresponding unit (so-called unit characters) in the A. The numerical value and the unit symbol are both factors whose product is the physical size. However, size has itself neither a particular associated numerical value nor a particular associated unit; as with any product, there are many different combinations of numerical value and unit, the same size found (Example: A = 300 · m = 0.3 · km = ...). Therefore, it is pointless either specify only the numeric value or just the unit.

The value of a quantity is independent of the chosen unit that describes the size, and must be kept by the numerical value of the size apart when the size is expressed in a particular unit. The above notation with curly braces could be extended with a unit symbol index to illustrate the dependence (example: { λ } m = 6.982 × 10-7 or equivalently { λ } = 698.2 nm ). In practice, where it is necessary to mention the numerical value of a, expressed in a particular unit size, it is more appropriate to the size to be divided by the unit (for example, λ / m = 6.982 × 10-7 and λ / nm = 698.2 ). This is a particularly useful and widely used notation to label the axes of a graph or a table header, because the repetition of the unit character after each numerical value is typographically often inappropriate.

Typographic Conventions

Symbols for sizes

• Sizes are usually represented by an icon that comes from a single letter of the Latin or Greek alphabet.

• Symbols for quantities are italic - regardless of typestyle to be used in the rest of the text.

• If in a text different sizes represented by the same symbol, they can be distinguished from each other by deep position.

• A subscript is only printed in italics when it consists of a symbol of a size or a variable. Other subscripts are printed upright. For example, Vn can be the symbol of a nominal volume; n is an abbreviation here. In contrast, the n in Vn is a running index.

Names for units and symbols

• If an internationally standardized unit symbols exist, this sign should be used exclusively. Today, the International System of Units ( SI) is the world's most widely used system of units of physical quantities. This distinction is made between uppercase and lowercase characters unit. For example, the prefix k for kilo while K stands for Kelvin. SI unit characters that have been named after a person or a place that begin with a capital letter, as well as all the prefixes mega upwards. All other characters are lowercase. The only exception is the sign of liters, which can be both small - and large written ( l and L). However, it is checked by the CIPM at the time, if one of the two options can not be abolished.

• Unit characters are printed upright.

Pay

• Numbers are printed upright.

• ISO 31-0 specifies in Annex 2 that the decimal separator is either a comma or the point on the base line. This decision follows the tenth resolution of the 22nd General Conference of Weights and Measures.

• Numbers from a longer sequence of digits can be made more readable if they are divided by narrow spaces in groups (preferably groups of three ). ISO 31-0 specifies that such groups of digits should never be separated by commas or periods, as these are reserved for use as the decimal separator.

• For numbers whose size is less than one, should precede the decimal is the number zero.

• The multiplication sign is either a cross ( x ) or a point halfway up ( · ), the latter should not be used if the point is used as the decimal separator, to avoid confusion between the decimal point and the multiplication sign.

Expressions

• If a lot of words, it follows the unit symbol on the numeric value (example: 12 km).

• Unit character and value are separated by a space. This rule also applies to the symbol ° C for degrees Celsius ( Example: 14 ° C). The only exceptions are the unit characters degrees (°), minutes (') and seconds ( " ) of plane angles without a space on the numerical values ​​follow (Example: 180 °).

• If variables are added or subtracted, so brackets can be used to distribute the unit symbol over several numerical values. Examples:

• Products can as from, a b, a ⋅ b or a × b are written.

• Divisions can be used as, a / b, or as the product of A and B -1 ( a ⋅ b-1) are written. Numerator and denominator can be products or quotients myself, but in this case, should the slash (/) followed by no multiplication or division sign on the same line, unless parentheses are used to avoid ambiguity.