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SI Unit rules and style conventions
Check List for Reviewing Manuscripts

  #1                  Only units of the SI and those units recognized for use with the SI are used to
    General           express the values of quantities. Equivalent values in other units are given in
                      parentheses following values in acceptable units only when deemed necessary for
                      the intended audience.

  #2              Abbreviations such as sec, cc, or mps are avoided and only standard unit
    Abbreviations symbols, prefix symbols, unit names, and prefix names are used.

                               proper: s or second; cm3 or cubic centimeter; m/s or meter per second
                            improper: sec; cc; mps

  #3                  Unit symbols are unaltered in the plural.
    Plurals
                              proper: l = 75 cm
                            improper: l = 75 cms

  #4                  Unit symbols are not followed by a period unless at the end of a sentence.
    Punctuation
                              proper: The length of the bar is 75 cm.
                                      The bar is 75 cm long.
                            improper: The bar is 75 cm. long.

   #5              A space or half-high dot is used to signify the multiplication of units. A solidus
    Multiplication (i.e., slash), horizontal line, or negative exponent is used to signify the division
    & division     of units. The solidus must not be repeated on the same line unless parentheses are
                   used.
                              proper: The speed of sound is about 344 m·s-1 (meters per second)
                                      The decay rate of 113Cs is about 21 ms-1 (reciprocal
                                      milliseconds)
                                      m/s, m·s-2, m·kg/(s3·A), m·kg·s-3·A-1
                                      m/s, m s-2, m kg/(s3 A), m kg s-3 A-1
                            improper: The speed of sound is about 344 ms-1 (reciprocal milliseconds)
                                      The decay rate of 113Cs is about 21 m·s-1 (meters per second)
                                      m ÷ s, m/s/s, m·kg/s3/A

  #6                  Variables and quantity symbols are in italic type. Unit symbols are in roman
    Typeface          type. Numbers should generally be written in roman type. These rules apply
                      irrespective of the typeface used in the surrounding text. For more details, see
                   Typefaces for symbols in scientific manuscripts
                            proper: She exclaimed, "That dog weighs 10 kg!"
                                    t = 3 s, where t is time and s is second
                                    T = 22 K, where T is thermodynamic temperature, and K is
                                    kelvin
                         improper: He exclaimed, "That dog weighs 10 kg!
                                   t = 3 s, where t is time and s is second
                                   T = 22 K, where T is thermodynamic temperature, and K is
                                   kelvin

#7                 Superscripts and subscripts are in italic type if they represent variables,
  Typeface         quantities, or running numbers. They are in roman type if they are descriptive.

                   subscript category typeface proper usage
                              quantity italic c p, specific heat capacity at constant pressure
                           descriptive roman mp, mass of a proton
                       running number         italic


#8              The combinations of letters "ppm," "ppb," and "ppt," and the terms part per
  Abbreviations million, part per billion, and part per trillion, and the like, are not used to express
                the values of quantities.
                             proper: 2.0 µL/L; 2.0 x 10-6 V;
                                     4.3 nm/m; 4.3 x 10-9 l;
                                     7 ps/s; 7 x 10-12 t,
                                     where V, l, and t are the quantity symbols for volume, length,
                                     and time.
                          improper: "ppm," "ppb," and "ppt," and the terms part per million, part per
                                    billion, and part per trillion, and the like

#9              Unit symbols (or names) are not modified by the addition of subscripts or other
  Unit          information. The following forms, for example, are used instead.
  modifications
                        proper: V max = 1000 V
                                 a mass fraction of 10 %
                          improper: V= 1000 Vmax
                                    10 % (m/m) or 10 % (by weight)

#10              The symbol % is used to represent simply the number 0.01.
  Percent
                    proper: l1 = l2(1 + 0.2 %), or
                            D = 0.2 %,
                             where D is defined by the relation D = (l1 - l2)/l2.

                 improper: the length l1 exceeds the length l2 by 0.2 %

#11             Information is not mixed with unit symbols or names.
  Information
  & units          proper: the water content is 20 mL/kg
                 improper: 20 mL H2O/ kg
                           20 mL of water/ kg

#12             It is clear to which unit symbol a numerical value belongs and which mathematical
  Math          operation applies to the value of a quantity.
  notation
                   proper: 35 cm x 48 cm
                           1 MHz to 10 MHz or (1 to 10) MHz
                           20 °C to 30 °C or (20 to 30) °C
                           123 g ± 2 g or (123 ± 2) g
                           70 % ± 5 % or (70 ± 5) %
                           240 x (1 ± 10 %) V
                 improper: 35 x 48 cm
                           1 MHz-10 MHz or 1 to 10 MHz
                           20 °C-30 °C or 20 to 30 °C
                           123 ± 2 g
                           70 ± 5 %
                           240 V ± 10 % (one cannot add 240 V and 10 %)

#13             Unit symbols and unit names are not mixed and mathematical operations are not
  Unit          applied to unit names.
  symbols
  & names          proper: kg/m3, kg · m-3, or kilogram per cubic meter
                 improper: kilogram/m3, kg/cubic meter, kilogram/cubic meter, kg per m3, or
                           kilogram per meter3.

#14          Values of quantities are expressed in acceptable units using Arabic numerals and
  Numerals & symbols for units.
  unit
  symbols       proper: m = 5 kg
                         the current was 15 A
                 improper: m = five kilograms
                           m = five kg
                           the current was 15 amperes

#15             There is a space between the numerical value and unit symbol, even when the value
  Unit          is used in an adjectival sense, except in the case of superscript units for plane angle.
  spacing
                   proper: a 25 kg sphere
                           an angle of 2° 3' 4"
                            If the spelled-out name of a unit is used, the normal rules of English
                            apply: "a roll of 35-millimeter film."
                improper: a 25-kg sphere
                          an angle of 2 ° 3 ' 4 "

#16            The digits of numerical values having more than four digits on either side of the
  Digit        decimal marker are separated into groups of three using a thin, fixed space counting
  spacing      from both the left and right of the decimal marker. Commas are not used to
               separate digits into groups of three.
                  proper: 15 739.012 53
               improper: 15739.01253
                         15,739.012 53

#17            Equations between quantities are used in preference to equations between
  Quantity     numerical values, and symbols representing numerical values are different from
  equations    symbols representing the corresponding quantities. When a numerical-value
               equation is used, it is properly written and the corresponding quantity equation is
               given where possible.
                  proper: (l/m) = 3.6-1 [v/(km/h)](t/s)
               improper: l = 3.6-1 vt, accompanied by text saying,
                         "where l is in meters, v is in kilometers per second, and t is in seconds"

#18            Standardized quantity symbols are used. Similarly, standardized mathematical
  Standard     signs and symbols are used. More specifically, the base of "log" in equations is
  symbols      specified when required by writing loga x (meaning log to the base aof x),
               lb x (meaning log2 x), ln x (meaning loge x), or lg x (meaning log10 x).

                  proper: tan x
                          R for resistance
                          Ar for relative atomic mass

                improper: tg x for tangent of x
                          words, acronyms, or ad hoc groups of letters

#19            When the word "weight" is used, the intended meaning is clear. (In science and
  Weight vs.   technology, weight is a force, for which the SI unit is the newton; in commerce and
  mass         everyday use, weight is usually a synonym for mass, for which the SI unit is the
               kilogram.)

#20            A quotient quantity is written explicitly.
  Quotient
  quantity        proper: mass divided by volume
                improper: mass per unit volume
  #21          An object and any quantity describing the object are distinguished. (Note the
    Object &   difference between "surface" and "area," "body" and "mass," "resistor" and
    quantity   "resistance," "coil" and "inductance.")
                  proper: A body of mass 5 g
                improper: A mass of 5 g

  #22          The obsolete terms normality, molarity, and molal and their symbols N, M, and m
    Obsolete   are not used.
    Terms
                  proper: amount-of-substance concentration of B (more commonly called
                          concentration of B), and its symbol cB and SI unit mol/m3 (or a related
                          acceptable unit)
                          molality of solute B, and its symbol bB or mB and SI unit mol/kg (or a
                          related unit of the SI)
                improper: normality and the symbol N, molarity and the symbol M
                          molal and the symbol m



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