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Information about Iso 31 0

ISO 31-0 is the introductory part of international standard ISO 31 on quantities and units. It provides guidelines for using physical quantities, quantity and unit symbols, and coherent unit systems, especially the SI. It is intended for use in all fields of science and technology and is augmented by more specialized conventions defined in other parts of the ISO 31 standard.

Scope

ISO 31 covers only physical quantities used for the quantitative description of physical phenomena. It does not cover conventional scales (e.g., Beaufort scale, Richter scale, colour intensity scales), results of conventional tests, currencies, or information content. The presentation here is only a brief summary of some of the detailed guidelines and examples given in the standard.

Quantities and units

Physical quantities can be grouped into mutually comparable categories. For example, length, width, diameter and wavelength are all in the same category, that is they are all quantities of the same kind. One particular example of such a quantity can be chosen as a reference quantity, called the unit, and then all other quantities in the same category can be expressed in terms of this unit, multiplied by a number called the numerical value. For example, if we write

the wavelength is λ = 6.982 × 10−7 m


then "λ" is the symbol for the physical quantity (wavelength), "m" is the symbol for the unit (metre), and "6.982 × 10−7" is the numerical value of the wavelength in metres.

More generally, we can write

A = {A} · [A]


where A is the symbol for the quantity, {A} symbolizes the numerical value of A, and [A] represents the corresponding unit in which A is expressed here. Both the numerical value and the unit symbol are factors, and their product is the quantity. A quantity itself has no inherent particular numerical value or unit; as with any product, there are many different combinations of numerical value and unit that lead to the same quantity (e.g., A = 300 · m = 0.3 · km = ...). This ambiguity makes the {A} and [A] notations useless, unless they are used together.

The value of a quantity is independent of the unit chosen to represent it. It must be distinguished from the numerical value of the quantity that occurs when the quantity is expressed in a particular unit. The above curly-bracket notation could be extended with a unit-symbol index to clarify this dependency, as in {λ}m = 6.982 × 10−7 or equivalently {λ}nm = 698.2. In practice, where it is necessary to refer to the numerical value of a quantity expressed in a particular unit, it is notationally more convenient to simply divide the quantity through that unit, as in

λ/m = 6.982 × 10−7


or equivalently

λ/nm = 698.2.


This is a particularly useful and widely used notation for labeling the axes of graphs or for the headings of table columns, where repeating the unit after each numerical value can be typographically inconvenient.

Typographic conventions

Symbols for quantities

  • Quantities are generally represented by a symbol formed from single letters of the Latin or Greek alphabet.
  • Symbols for quantities are set in italic type, independent of the type used in the rest of the text.
  • If in a text different quantities use the same letter symbol, they can be distinguished via subscripts.
  • A subscript is only set in italic type if it consists of a symbol for a quantity or a variable. Other subscripts are set in upright (roman) type. For example, write Vn for a "nominal volume" (where "n" is just an abbreviation for the word "nominal"), but write Vn if n is a running index number.

Names and symbols for units

Main articles: SI, SI base unit, SI derived unit, and SI prefix
  • If an internationally standardized symbol exists for a unit, then only that symbol should be used. See the SI articles for the list of standard symbols defined by the International System of Units. Note that the distinction between uppercase and lowercase letters is significant for SI unit symbols. For example, "k" is the prefix kilo and "K" stands for the unit kelvin. The symbols of all SI units named after a person start with an uppercase letter, as do the symbols of all prefixes from mega on upwards. All other symbols are lowercase; the only exception is litre, where both l and L are allowed.
  • Symbols for units should be printed in an upright (roman) typeface.

Numbers

  • Numbers should be printed in upright (roman) type.
  • ISO 31-0 specifies that "the decimal sign is a comma on the line". It notes that in English documents a dot on the line is also commonly used. (Unconfirmed rumors state that ISO has changed its view on this matter http://www.nist.gov/public_affairs/techbeat/tb2006_1122.htm#decimal and that it now recognize the decimal comma and the decimal dot as equal alternatives.)
  • Numbers consisting of long sequences of digits can be made more readable by separating them into groups, preferably groups of three, separated by a small space. For this reason, ISO 31-0 specifies that such groups of digits should never be separated by a comma or point, as these are reserved for use as the decimal sign.
  • For numbers whose magnitude is less than 1, the decimal sign should be preceded by a zero.

Expressions

  • Unit symbols follow the numerical value in the expression of a quantity.
  • Numerical value and unit symbol are separated by a space. This rule also applies to the symbol "°C" for degrees Celsius, as in "25 °C". The only exception are the symbols for the units of plane angle degree, minute and second, which follow the numerical value without a space inbetween (for example "30°").
  • Where quantities are added or subtracted, parenthesis can be used to distribute a unit symbol over several numerical values, as in
T = 25 °C − 3 °C = (25 − 3) °C
P = 100 kW ± 5 kW = (100 ± 5) kW
(but not: 100 ± 5 kW)
d = 12 × (1 ± 10−4) m
  • Products can be written as ab, a b, a⋅b, or a×b. The sign for multiplying numbers is a cross (×) or a half-height dot (⋅). The cross should be used adjacent to numbers if a dot on the line is used as the decimal separator, to avoid confusion between a decimal dot and a multiplication dot.
  • Division can be written as , a/b, or by writing the product of a and b−1, for example a⋅b−1. Numerator or denominator can themselves be products or quotients, but in this case, a solidus (/) should not be followed by a multiplication sign or division sign on the same line, unless parentheses are used to avoid ambiguity.

Mathematical signs and symbols

A comprehensive list of internationally standardized mathematical symbols and notations can be found in ISO 31-11.

See also

References

International Organization for Standardization (Organisation internationale de normalisation), widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations.
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International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide.
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A physical quantity is either a physical property that can be measured (e.g. mass, volume, etc.), or the result of a measurement. The value of a physical quantity Q is expressed as the product of a numerical value and a physical unit [Q].
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units of measurement have played a crucial role in human endeavour from early ages up to this day. Disparate systems of measurement used to be very common. Now there is a global standard, the International System (SI) of units, the modern form of the metric system.
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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
  • One of two Italian words:
  • sì (accented) for "yes"
  • si

..... Click the link for more information.
International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide.
..... Click the link for more information.
A physical quantity is either a physical property that can be measured (e.g. mass, volume, etc.), or the result of a measurement. The value of a physical quantity Q is expressed as the product of a numerical value and a physical unit [Q].
..... Click the link for more information.
The adjective conventional may be used in the sense of
  • ordinary, unexceptional, as expected now
  • agreed according to a convention (norm)
  • conventional weapon, one which does not incorporate chemical, biological or nuclear payloads

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The Beaufort scale is an empirical measure for describing wind velocity based mainly on observed sea conditions. Its full name is the Beaufort wind force scale.

History


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The richter magnitude scale, or more correctly local magnitude ML scale, assigns a single number to quantify the amount of seismic energy released by an earthquake.
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In typography, italic type refers to cursive typefaces based on a stylized form of calligraphic handwriting. The influence from calligraphy can be seen in their usual slight slanting to the right.
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In Typography, "roman" type has two principal meanings, both stemming from the stylistic origin of text typefaces from inscriptional capitals used in ancient Rome:
  • one of the major families of traditional typefaces as a synonym for serif or antiqua fonts.

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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
  • One of two Italian words:
  • sì (accented) for "yes"
  • si

..... Click the link for more information.
The international system (SI) of units defines seven SI base units: physical units defined by an operational definition.

All other physical units can be derived from these base units: these are known as SI derived units. Derivation is by dimensional analysis.
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SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.

Dimensionless derived units

The following SI units are actually dimensionless ratios, formed by dividing two identical SI units.
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An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple.
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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
  • One of two Italian words:
  • sì (accented) for "yes"
  • si

..... Click the link for more information.
The litre or liter (see spelling differences) is a unit of volume. There are two official symbols, namely the Latin letter L both in lower and upper case: l and L.
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In Typography, "roman" type has two principal meanings, both stemming from the stylistic origin of text typefaces from inscriptional capitals used in ancient Rome:
  • one of the major families of traditional typefaces as a synonym for serif or antiqua fonts.

..... Click the link for more information.
In Typography, "roman" type has two principal meanings, both stemming from the stylistic origin of text typefaces from inscriptional capitals used in ancient Rome:
  • one of the major families of traditional typefaces as a synonym for serif or antiqua fonts.

..... Click the link for more information.
ISO 31-11 is the part of international standard ISO 31 that defines mathematical signs and symbols for use in physical sciences and technology.

Its definitions include:

Mathematical logic


Sign Example Name Meaning and verbal equivalent Remarks
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International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide.
..... Click the link for more information.
International standard ISO 1000 (SI units and recommendations for the use of their multiples and of certain other units, International Organization for Standardization, 1992) is the ISO standard describing the International System of Units (SI).
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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
  • One of two Italian words:
  • sì (accented) for "yes"
  • si

..... Click the link for more information.
The term International Standard may refer to
  • International standard
  • International Standard (dance), a category of ballroom dance


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International Organization for Standardization (Organisation internationale de normalisation), widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations.
..... Click the link for more information.
The International Union of Pure and Applied Chemistry (IUPAC) (IPA: [aɪ ju pæk]) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry.
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The International Union of Pure and Applied Chemistry (IUPAC) (IPA: [aɪ ju pæk]) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry.
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The National Institute of Standards and Technology (NIST), known between 1901–1988 as the National Bureau of Standards (NBS), is a non-regulatory agency of the United States Department of Commerce. The institute's mission is to promote U.S.
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