Rules and Style Conventions for Expressing Values of Quantities. Thompson, A. and Taylor, B. N. In Guide for the Use of the International System of Units (SI), volume 811, of Special Publication Series, pages 15–23. National Institute of Standards and Technology (NIST).
Rules and Style Conventions for Expressing Values of Quantities [link]Paper  abstract   bibtex   
[Excerpt: Value and numerical value of a quantity] The value of a quantity is its magnitude expressed as the product of a number and a unit, and the number multiplying the unit is the numerical value of the quantity expressed in that unit. [] More formally, the value of quantity A can be written as A = {A}[A], where {A} is the numerical value of A when the value of A is expressed in the unit [A]. The numerical value can therefore be written as {A} = A / [A], which is a convenient form for use in figures and tables. Thus, to eliminate the possibility of misunderstanding, an axis of a graph or the heading of a column of a table can be labeled "t/°C" instead of "t (°C)" or "Temperature (°C)." Similarly, an axis or column heading can be labeled "E/(V/m)" instead of "E (V/m)" or "Electric field strength (V/m)." [] [...] [Space between numerical value and unit symbol] In the expression for the value of a quantity, the unit symbol is placed after the numerical value and a space is left between the numerical value and the unit symbol. [] The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle: °, ', and ", respectively (see Table 6), in which case no space is left between the numerical value and the unit symbol. [] [...] [Symbols for numbers and units versus spelled-out names of numbers and units] This Guide takes the position that the key elements of a scientific or technical paper, particularly the results of measurements and the values of quantities that influence the measurements, should be presented in a way that is as independent of language as possible. [] [...] [:percentage by, fraction] In keeping with Ref. [4: ISO 31-0], this Guide takes the position that it is acceptable to use the internationally recognized symbol % (percent) for the number 0.01 with the SI and thus to express the values of quantities of dimension one (see Sec. 7.14) with its aid. When it is used, a space is left between the symbol % and the number by which it is multiplied [4: ISO 31-0]. [] [...] [:ppm, ppb, and ppt] In keeping with Ref. [4: ISO 31-0], this Guide takes the position that the language-dependent terms part per million, part per billion, and part per trillion, and their respective abbreviations "ppm," "ppb," and "ppt" (and similar terms and abbreviations), are not acceptable for use with the SI to express the values of quantities. [] [...] [Distinction between an object and its attribute] To avoid confusion, when discussing quantities or reporting their values, one should distinguish between a phenomenon, body, or substance, and an attribute ascribed to it. [] [...]
@incollection{thompsonRulesStyleConventions2008,
  title = {Rules and Style Conventions for Expressing Values of Quantities},
  booktitle = {Guide for the Use of the {{International System}} of {{Units}} ({{SI}})},
  author = {Thompson, Ambler and Taylor, Barry N.},
  date = {2008},
  volume = {811},
  pages = {15--23},
  publisher = {{National Institute of Standards and Technology (NIST)}},
  url = {http://www.webcitation.org/6kuETIpuv},
  abstract = {[Excerpt: Value and numerical value of a quantity]

The value of a quantity is its magnitude expressed as the product of a number and a unit, and the number multiplying the unit is the numerical value of the quantity expressed in that unit.

[] More formally, the value of quantity A can be written as A = {A}[A], where {A} is the numerical value of A when the value of A is expressed in the unit [A]. The numerical value can therefore be written as {A} = A / [A], which is a convenient form for use in figures and tables. Thus, to eliminate the possibility of misunderstanding, an axis of a graph or the heading of a column of a table can be labeled "t/°C" instead of "t (°C)" or "Temperature (°C)." Similarly, an axis or column heading can be labeled "E/(V/m)" instead of "E (V/m)" or "Electric field strength (V/m)."

[] [...]

[Space between numerical value and unit symbol]

In the expression for the value of a quantity, the unit symbol is placed after the numerical value and a space is left between the numerical value and the unit symbol.

[] The only exceptions to this rule are for the unit symbols for degree, minute, and second for plane angle: °, ', and ", respectively (see Table 6), in which case no space is left between the numerical value and the unit symbol.

[] [...]

[Symbols for numbers and units versus spelled-out names of numbers and units]

This Guide takes the position that the key elements of a scientific or technical paper, particularly the results of measurements and the values of quantities that influence the measurements, should be presented in a way that is as independent of language as possible. 

[] [...]

[:percentage by, fraction]

In keeping with Ref. [4: ISO 31-0], this Guide takes the position that it is acceptable to use the internationally recognized symbol \% (percent) for the number 0.01 with the SI and thus to express the values of quantities of dimension one (see Sec. 7.14) with its aid. When it is used, a space is left between the symbol \% and the number by which it is multiplied [4: ISO 31-0].

[] [...]

[:ppm, ppb, and ppt]

In keeping with Ref. [4: ISO 31-0], this Guide takes the position that the language-dependent terms part per million, part per billion, and part per trillion, and their respective abbreviations "ppm," "ppb," and "ppt" (and similar terms and abbreviations), are not acceptable for use with the SI to express the values of quantities. 

[] [...]

[Distinction between an object and its attribute]

To avoid confusion, when discussing quantities or reporting their values, one should distinguish between a phenomenon, body, or substance, and an attribute ascribed to it.

[] [...]},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14149492,dimensional-analysis,metrology,notation,percent,physics,ppm,semantics,si},
  series = {Special {{Publication}} Series}
}
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