Post 16: Symbols, quantities, units and abbreviated terms

Quantities, units and their symbols, graphical symbols and abbreviated terms are widely used in European Standards with technical content, and they are very helpful to ease the reading of the standard. However, there are many different ways to write the same thing! This is why the rules for drafting European Standards (Internal Regulations Part 3) require symbols and abbreviated terms to be consistent in all standards. Using relevant excerpts from the Internal Regulations Part 3, this post will give an overview of the provisions available to reach that target:

      ·         How and where do I give the explanation of symbols and abbreviated terms?
      ·         How do I write quantities, units, symbols and abbreviated terms?
      ·         Which symbols and units can be used (and which ones should be avoided)?
      ·         What about graphical symbols?
      ·         Where can I find more documentation ?

How and where do I give the explanation of symbols and abbreviated terms?

The explanation of symbols and abbreviated terms necessary for the understanding of the document may be centralized in a separate clause, but it is also possible to combine it with the terms and definitions (e.g. "Terms, definitions, symbols, units and abbreviated terms").

EXAMPLE 1

3              Terms, definitions, symbols, units and abbreviated terms
3.1          Terms and definitions
………
3.2          Symbols, units and abbreviated terms
………

When a separate clause is necessary, it is preferable to place it just after the terms and definitions clause. It is recommended to list the symbols and abbreviated terms in alphabetical order, with upper case letters before lower case letters, and Latin letters before Greek letters.

The explanations can also be scattered throughout the text, in defined terms, after formulae (see our blog 14 about formulae) or in a figure key.

If a list of abbreviated terms is not given in the document, then the first time that an abbreviated term is used, the full term shall be given with the abbreviated term following in parentheses.

When the symbol or abbreviated term is included in a definition, it shall be placed on a new line after the preferred term. Information regarding the units applicable to a quantity shall be given in a note to entry.

EXAMPLE 2

3.2.6
measuring distance
r₁
shortest distance from the surface of the appliance to the closest point of the sensor surface

Note 1 to entry:            The measuring distance is expressed in metres.

How do I write quantities, units, symbols and abbreviated terms?

When a sentence begins with an abbreviated term, which, within the sentence, would consist of several lower case letters, all the letters of the abbreviated term shall be capital letters, for example 'A.C.'.

Unit symbols shall always be in regular type and quantity symbols shall always be in italic type.

Symbols representing numerical values shall be different from symbols representing the corresponding quantities.

Space or no space ? The rule is simple: Almost all unit symbols shall be preceded by a space, with one exception: the unit symbols for degree, minute and second for plane angle shall immediately follow the numerical value.

EXAMPLE             37,5 °C for temperature but 37°5' for an angle.

In a table, the units used in a given column shall generally be indicated under the column heading. As an exception to this rule, when all units are the same, a suitable statement (for example, 'Dimensions in millimetres') shall instead be placed above the right-hand corner of the table.

In the same way, when all units for a quantity are the same in a figure, a suitable statement shall be placed above the right-hand corner of the figure.

See examples in our blogs 10 and 12 about tables and figures.

 

Which symbols and units can be used (and which ones should be avoided)?

Provisions regarding the use of symbols, abbreviated terms and units are too detailed to be fully reported here. Extensive information is available in the Internal Regulations Part 3, and in particular in its Annex I.

Amongst others provisions, let us highlight the need to use the International System of Units (SI) (ISO 80000 and IEC 80000) and a few additional units, namely minute (min), hour (h), day (d), degree (°), minute ('), second (''), litre (l), tonne (t).

Also, did you know that 'hrs', 'sec', 'rpm', 'ppm' and 'ppb' are not allowed in European Standards?

What about graphical symbols ?

Graphical symbols shall be in accordance with relevant standards, e.g. IEC 60417, IEC 60617, ISO 14617 and ISO 7000.  They need to be language neutral.

The use of graphical symbols in standards is coordinated by:

       ·         ISO/TC 145 "Graphical symbols",

       ·         ISO/TC 10 "Technical product documentation",

in collaboration with

       ·         IEC/TC 3 "Information structures, documentation and graphical symbols" and

       ·         IEC/TC 3/SC 3C "Graphical symbols for use on equipment".

The aim is to ensure that one symbol does not have more than one meaning and that the same meaning is not covered by more than one symbol.

Therefore, it is very important that a Technical Body contact the above TCs when preparing ENs that include graphical symbols.

Symbols already standardized are registered in the basic ISO catalogue standards and in the relevant database (available on the ISO Online Browsing Platform (OBP)).

It is an absolute requirement to use at least the registration number in every publication as a means of identification (e.g. ISO 7000-1135 or ISO 7010-W001).

EXAMPLE

 

 
 

Where can I find documentation?

Not enough with the above?

The Internal Regulations Part 3 provides a lot of information, in particular in the following clauses and annexes. Let's follow the guide:

·	6.3.2	Symbols and abbreviated terms with provisions about the sorting
·	6.6.2	Spelling and abbreviation of names of organizations, style, reference works and abbreviated terms
·	6.6.6.4	Units in tables
·	6.6.5.5	Choice of letter symbols, style of lettering, and labelling
·	6.6.5.6 & 6.6.5.7	Graphical symbols in mechanical engineering drawings and in diagrams
·	6.6.9	Quantities, units, symbols and signs
·	6.6.11	Values, dimensions and tolerances
·	B.5	List of International Standards on Quantities, units and their symbols
·	B.6	List of International Standards on Abbreviated terms
·	B.10 & B.22	List of International Standards on Graphical symbols, public information symbols and safety signs
·	D.4.2 & D.4.8	Symbols and abbreviated terms in definitions, Symbols for quantities and units in definitions
·	Annex I	Detailed but useful information on quantities and units

Regarding graphical symbols, a guidance document is available on the CEN website (Home page > Quick links > Business Operations Support System (BOSS) > Reference material > Guidance documents > Drafting Guidance > Graphical symbols).

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Next week: A little bit more about hanging paragraphs, clause numbering and lists …

 

Anne Clausse (aclausse@cencenelec.eu)

 

 

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