Equivalent
values in other units can be given in brackets following values
in acceptable units, but only when deemed necessary for the intended
audience.
|
|
|
Example
of correct usage
|
Example
of improper usage
|
Abbreviations
|
Abbreviations
such as sec, cc, or mps are to be avoided and only standard unit
symbols, prefix symbols, unit names, and prefix names are to be
used. |
s or second;
cm3 or cubic centimeter; m s-1, m/s or metre per second |
sec; cc; mps |
Plurals |
Unit symbols are unaltered in the plural.
|
l
= 75 cm |
l
= 75 cms |
Punctuation |
Unit symbols
are not followed by a period (full stop) unless at the end
of a sentence.
|
The length
of the bar is 75 cm.
The bar is 75 cm long. |
The
bar is 75 cm. long. |
Multiplication
and division |
A space or half-high dot is used to signify the multiplication of
units. A solidus (i.e., slash), horizontal line, or negative exponent
is used to signify the division of units. The solidus must not be
repeated on the same line unless parentheses (brackets) are used.
|
The speed
of the car is about 21 m·s-1 (metres 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
|
The
speed of the car is about 21 ms-1 (reciprocal milliseconds)
The decay rate of 113Cs is about 21 m s-1 (metres per
second)
m ÷ s, m/s/s, m·kg/s3/A |
Typeface
|
- Variables
and quantity symbols should be in italic type.
- Unit symbols
should be in roman type.
- Numbers
should generally be written in roman type.
These rules
apply irrespective of the typeface used in the surrounding text
or when submitting hand written work your handwriting style!
This also
applies to sub and superscripts.
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|
|
Abbreviations |
The combinations
of letters "ppm," "ppb," and "ppt," and the terms part per million, part per billion, and part per trillion,
and the like, are not used to express the values of quantities.
|
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. |
"ppm," "ppb," and "ppt,"
and the terms part per million, part per billion, and part per trillion,
and suchlike |
Unit
modifications |
Unit symbols
(or names) are not to be modified by the addition of subscripts
or other information. |
Vmax = 1000
V |
V=
1000 Vmax |
Percent |
The symbol
% is used to represent simply the number 0.01 |
l1
= l2(1 + 0.2 %), or
D = 0.2 %, where D is defined by the relation D = (l1
- l2)/l2. |
The
length l1 exceeds the length l2 by 0.2 % |
Information
and units |
Information
should not be mixed with unit symbols or names.
|
the water content
is 20 ml/kg |
20
mL H2O/ kg
20 ml of water/ kg |
Mathematical
notation |
It must be clear to which unit symbol a numerical value belongs
and which mathematical operation applies to the value of a quantity.
|
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 |
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 %) |
Unit symbols
and names |
Unit symbols and unit names should not be mixed and mathematical
operations should not be applied to unit names. |
kg/m3,
kg · m-3, or kilogram per cubic metre |
kilogram/m3,
kg/cubic metre, kilogram/cubic metre, kg per m3, or kilogram
per metre3. |
Numerals
and
unit symbols |
Values of quantities
are expressed in acceptable units using Arabic numerals and symbols
for units. |
m = 5 kg
the current was 15 A |
m
= five kilograms
m = five kg
the current was 15 amperes |
Unit
spacing |
There is
a space between the numerical value and unit symbol, even
when the value is used in an adjectival sense, except in the case
of superscript units for plane angle.
If the spelled-out
name of a unit is used, the normal rules of English apply:
|
a 25 kg sphere
an angle of 2° 3' 4"
"a roll
of 35-millimeter film."
|
a
25-kg sphere
an angle of 2 ° 3 ' 4 " |
Digit
spacing |
The digits of numerical values having more than four digits on either
side of the decimal marker are separated into groups of three
using a thin, fixed space counting from both the left and right
of the decimal marker. Commas are not used to separate digits into
groups of three.
|
15
739.012 53 |
15739.01253
15,739.012 53 |
Quantity
equations |
Equations
between quantities are used in preference to equations between numerical
values, and symbols representing numerical values are different
from 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.
|
|
|
Standard
symbols |
Standardized
quantity symbols are used. Similarly, standardized mathematical
signs and symbols are used. More specifically, the base of "log" in equations is specified when required by writing loga
x (meaning log to the base a of x), lb x (meaning log2
of x), ln x (meaning loge x), or lg x (meaning log10
x).
|
tan x
R for resistance
Ar for relative atomic mass |
tg
x for tangent of x
words,
acronyms, or ad hoc groups of letters
|
Weight vs.
mass |
When the word "weight" is used, the intended meaning must be clear.
(In science and technology, weight is a force, for which the SI
unit is the newton; in commerce and everyday use, weight is usually
a synonym for mass, for which the SI unit is the kilogram.) |
|
|
Quotient
quantity |
A quotient
quantity should be written explicitly. |
mass divided
by volume |
mass
per unit volume |
Object and
quantity |
An object
and any quantity describing the object are supposed to be distinguished
clearly. (Note the difference between "surface" and "area,"
"body" and "mass," "resistor" and
"resistance," "coil" and "inductance.")
|
A body of mass
5 g |
A
mass of 5 g |
Obsolete
Terms |
The obsolete
terms normality, molarity, and molal and their symbols N, M, and
m are not to be used.
|
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) |
normality
and the symbol N, molarity and the symbol M
molal and the symbol m |
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