UNIVERSITY OF HONG KONG
LIBRARY
This book was a gift
from
Hong Kong Government Secretariat
Printed and Published by the Government Printer, Hong Kong
Contents
Item No.
Page
INTRODUCTION
3
1
BASE UNITS
5
2
DERIVED UNITS
5
3
UNITS IN INTERNATIONAL USE
6
4
EXAMPLES OF METRIC UNITS IN COMMON USE
8
5
PREFIXES
5.1 SI - Decimal Language
5.2 Prefixes in Common Use
9
9
9
6
PRESENTATION OF SI EXPRESSIONS
6.1 Lower Case for Initial Letters for The Names of Units
6.2 Upper and Lower Case Letters for Symbols for Units
6.3 Use of Upper and Lower Case Letters for Symbols for Prefixes
6.4 No Full Stop After Symbols, No Plural Form
6.5 Spacing of Numerical Values and Symbolic Expressions
6.6 Multiplication - Combination of Symbols for Units
6.7 Division - Combination of Symbols for Units
6.8 Layout of Numbers
6.9 Numbers Less Than Unity
11
11
11
11
12
12
12
12
13
13
7
CONVENTIONS ASSOCIATED WITH THE USE OF SI
7.1 Restricted Use of 'centimetre'
7.2 Dual Dimensioning not to be used
7.3 The Hyphen
7.4 Rounding Off
7.5 'kilo' - Pronunciation
7.6 'kilo'-Misuse of the Term
13
13
14
14
14
15
15
8
ENGLISH/CHINESE TRANSLATIONS
15
9
SPECIAL INSTRUCTIONS FOR SECRETARIES,
STENOGRAPHERS AND TYPISTS
9.1' Capitals
9.2 Spacing
9.3 Product of Units
9.4 The word 'per'
9.5 Plurals
9.6 Full Stops
9.7 The Decimal Point
9.8 Grouping of Numbers
9.9 The Hyphen
9.10 Squares, Cubes etc.
16
16
17
17
17
17
17
17
18
18
18
Contents continued
Item No.
9.11
9.12
9.13
9.14
9.15
Page
The letter't' for tonne
The letter 'ell' for litre
Prefixes
Shorthand outlines
Some Everyday Metric Units
18
18
18
19
19
10
OFFICE STATIONERY
10.1 Paper Sizes
10.2 Envelope Sizes
20
20
21
11
DRAWING OFFICE PRACTICE
22
12
METRIC KNOWLEDGE-TEST YOURSELF
25
13
COMMON CONVERSION FACTORS
Inside back
cover
Introduction
In keeping with Government's policy to promote the adoption of a metric
system of units, more accurately known as International System of Units
(SI), all Government Departments have been advised to proceed with a
programme to adopt and implement the sole use of SI units in their routine
business and to incorporate such units in any legislation, codes of practice,
standing orders, standard documents and the like administered by or in use
in their Offices.
The changeover should be implemented as early as possible and even in the
most measurement intensive Departments, the process is expected to be
effectively completed within two or three years at the utmost
For most of us, there are very few units to adopt, these are mainly related
to length, area, volume and capacity, for a comparatively very few officers
there may also be those units related to force, pressure, energy and power.
It is very important that we develop mental concepts in our new measurement language. For instance, although few of us could accurately measure
out one pint of liquid (imperial pint or U.S. pint?) without the aid of a
measuring device, we nevertheless dp have some very rough idea as to the
quantity of liquid in a pint. Therefore if we are to adapt to the new system of
measurement we must try to impress in our minds a few reference points;
the following may be of assistance:
Reference Point
Approx. Value
LENGTH
Diameter of a
10 cent coin
20 millimetres
Width of clenched
hand across knuckle
100 millimetres
Width of hand with
fingers outspread
200 millimetres
Height from floor
to door handle
1 metre
MASS
Two paper clips
1 gram
50 cent coin
5 grams
A bottle of milk
(including bottle
of course)
500 grams
Base of telephone set
1 kilogram
One litre of water
1 kilogram
VOLUME
Contents of a large
bottle of soft drink
1 litre
Likewise, in adopting any new system, errors may occur through unfamiliarity in writing the new names and their symbols; there are internationally
agreed rules and conventions for writing down names and symbols of metric
units and for expressing numerical values, these have all been discussed in
this booklet and should be carefully studied and adopted.
1
BASE UNITS
The metric system which we are adopting in Hong Kong is known as the
System International (SI).
The system is based upon a set of base units - only 7 in number and from
which all known physical quantities can be derived.
In SI, every physical quantity has a given name of unit and a corresponding
internationally recognised symbol.
The seven base units are;
Quantity
Name
Symbol
Length
Mass (see Note (1))
Time
Thermodynamic
temperature
metre
kilogram (see Note (2))
second
kelvin (see Note (3))
(commonly used unit
is degree Celsius)
ampere
candela
mole
m
kg
s
K
Electric Current
Luminous Intensity
Amount of Substance
(°C)
A
cd
mol
As you can see, for most of us only the first three quantities and the degree
Celsius need concern us; the remainder will be used mainly by scientists and
engineers.
Notes:
1 Previously the term 'weight' was used; technically speaking 'weight' is
the force of gravity acting on a body.
2 The preferred modern spelling is kilogram not kilogramme. Likewise, gram,
milligram not gramme, milligramme.
3 Although the SI unit - kelvin is used for scientific and technological
purposes; for common practical purposes the degree Celsius (symbol °C)
is used. The temperature interval on the Celsius scale is identical with that
on the kelvin scale.
2
DERIVED UNITS
From the seven base units, any number of other units can be derived or built
up to express all the known quantities of matter that we may wish to express.
Imagine the base units as building blocks which you can arrange logically
into groupings to express the required quantity.
Derived units may be divided into three groups as described below:
a units derived from base units;
b derived units having special names;
c units derived from derived units having special names and from base units.
The first range of derived units are produced from products or quotients of
base units and the most common type of derived units in this group are the
units for:
Quantity
Name
Symbol
area
square metre
m2
volume
cubic metre
m3
speed
metre per second
m/s
acceleration
metre per second squared m/s2
density
kilogram per cubic metre
kg/m3
Examples of the second type of derived units (units having special names)
are such as the units for:
Quantity
Name
Symbol
Derivation
force
newton
N
kg.m/s2
pressure
pascal
Pa
N/m2
energy, heat work
joule
J
N.m
power
watt
W
J.s
frequency
hertz
Hz
1/s
Again note each unit has a name and internationally recognised symbol.
Examples of the third type of derived units (combinations of units with
special names and base units) are such as the units for:
Quantity
Name
Symbol
torque
newton metre
N.m
specific latent heat
joule per kilogram
J/kg
3
UNITS IN INTERNATIONAL USE
In addition to the base units and derived units of SI there are some other units,
which although they could be defined in terms of SI base units, are nevertheless in such common international use and of such practical importance as
to be retained for use alongside SI.
The most common ones are; the units of time, i.e. day, hour, minute; the
units of plane angular measurement, i.e. degree minute second; a unit of
area - hectare, a unit of volume - litre and a unit of mass - tonne.
Non-Si Units Decimally Based on SI Units
Quantity
Name of unit
Unit symbol
Definition
area
hectare
ha
1 ha =10 000 m2
volume
litre
(Motel)
f (litre)
mass
tonne
(Note 2)
t (tonne)
1 t =1 000 kg
(also 1 megagram)
mass per unit
length
tex
(Note 3)
tex
1 tex=10~ 6 kg/m
(also 1 cubic
decimetre)
Notes:
1 The litre is recognized by the International Committee of Weights and
Measures (CIPM), and forms multiples in the same manner as SI units.
2 The tonne is recognized by the CIPM. Decimal sub-multiples of tonnes
are not used, but decimal multiples are formed in the same manner as SI
units - For example: megatonne (Mt).
3 The tex is a unit used in the textile industry. The tex forms multiples in the
same manner as SI units - For example: decitex, dtex.
Nlon-SI Units of Practical Importance
There are certain units outside the SI which are nevertheless recognized by
the CIPM as having to be retained because of their practical importance.
Quantity
Name of unit
plane angle
degree
minute
second
time
day
minute
hour
temperature,
temperature
interval
degree
Celsius
length*
nautical mile
(international)
speed velocity*
knot
(international)
Unit symbol
d
min
h
*Related to nautical and aeronautical navigation and meteorology.
1 nautical m/7e= 1 852 m.
One knot is equal to one nautical mile per hour.
4
EXAMPLES OF METRIC UNITS IN COMMON USE
The units most commonly encountered in day-to-day use are those for
length, area, mass (weight) and volume, capacity, density and temperature.
The base or derived units for these (in bold type) and their multiples and
sub-multiples and some typical applications are:
Quantity
Name
Typical Application 8- Remarks
length
millimetre (mm)
engineering, building design and precision measurement
centimetre (cm)
body and cloth piece-goods measurement.
metre (m)
replaces foot and yard measurement,
kilometre (km)
road, air distances.
square metre (m2)
floor and land area.
hectare (ha)
(10000m2)
large areas, farms, reservoirs.
square
kilometre (km2)
larger land areas - Hong Kong Island,
Kowloon, New Territories.
milligram (mg)
medicines.
gram (g)
foodstuffs and items previously
weighed by the pound, ounce, catty
or tael.
kilogram (kg)
foodstuffs, body mass and mass
measures up to a tonne; items previously weighed by pound, catty or
picul.
tonne (t or Mg)
(the proper technical
term is megagram,
1 t=1 Mg)
items previously described in tons.
volume
cubic metre (m3)
excavation, concrete, aggregate, dams,
large tanks.
capacity
litre (/)
small tanks, petrol, oil, wine, milk, beer.
area
mass
(onethousandth
part of a cubic
metre)
8
Name
Typical Application 8- Remarks
millilitre (ml)
(1 ml =1 cm3)
medicine, extracts, juices, bottled and
canned liquids.
kilogram per
cubic metre
(kg/m3)
building materials.
gram per litre (g//)
laboratory calculations,
gram per millilitre
(9/ml)
laboratory calculations.
temperature
degree Celsius
weather reports and common practical
temperature usages.
speed
metre per second
(m/s)
flow in pipelines, cutting speed and
speed of escalators and hoists.
kilometre per hour
(km/h)
road speeds.
Quantity
density
energy
joule (J)
kilojoule (kJ)
power
watt (W)
kilowatt (kW)
pressure
pascal (Pa)
kilopascal (kPa)
5
energy value of foods (replace the
calorie)
small electrical appliances and motors,
electric heaters, air conditioners, refrigerators.
tyre pressures, water pressure, pressure
gauges.
PREFIXES
5.1 Si-Decimal language
In SI, by using a decimal system of prefixes we can in simple language
describe the size of the unit in terms of multiples or sub-multiples of ten, e.g.
ten, one hundred, one thousand, one million and so on upwards or one tenth,
one hundredth, one thousandth, one millionth and likewise downwards.
We can thus avoid all the confusing and inconsistent factors we meet in
other systems such as 12, 3, 36, 66, 440, 1 760 etc. related to units of
length, and 16, 14, 112, 2 240 etc. related to units of weight.
5.2 Prefixes in common use
In SI these power increments or decrements are called 'prefixes' and each
has been given a name which when applied to the name of the physical
quantity being described indicates the magnitude of the unit in terms of a
power of 10. For example, the prefix kilo means 'one thousand' thus kilometre
(one thousand metres), kilogram (one thousand grams).
The following table shows the full range of prefixes and their numerical
factors, ranging from 10*18 to 10~18, those printed in bold type are the ones
which we find in most common use, indeed the vast majority of us will only
normally use kilo, centi and milli.
Just like units for quantities in SI, note that each prefix has been given a
name and an internationally recognised symbol.
PREFIXES
Name
Symbol
Value expressed
in terms of the
power of W
Value
1 000 000 000 000 000 000.0
E
1 000 000 000 000 000.0
P
1 000000000000.0
T
1 000 000 000.0
G
1 000 000.0
mega
M
1 000.0
kilo
k
h
hecto
100.0
da
deca
10.0
example 10 000 metres=10 kilometres=10 km
deci
d
0.1
cent!
c
0.01
milli
m
0.001
micro
ji
0.000 001
nano
n
0.000000001
pico
p
0.000000000001
femto
f
0.000 000 000 000 001
atto
a
0.000 000 000 000 000 001
example 0.032 metres=32 millimetres=32 mm
exa
peta
tera
1018
1Q16
1096
10
1032
10
10-12
10~
10~36
1010~912
10-10-15
10-18
Examples of prefixes in use are:
millimetre (mm)
=
10- 3 m =
0.001 metre
millilitre (ml)
--=
10~ 3 /
0.001 litre
milligram (mg)
=
10~3 g =
0.001 gram
kilometre (km)
=
103 m
=
1 000 metres
kilogram (kg)
= 103 g
==
1 000 grams
megagram (Mg) = 10 6 g
(commonly called 'tonne')
=*
1 000 000 grams or
1 000 kilograms
=
(Note: Spelling gram and kilogram NOT gramme and kilogramme)
10
6
PRESENTATION OF SI EXPRESSIONS
6.1 Lower case for initial letters for the names of units
The names of SI units start with a lower case (small) letter. (The only exception to this rule is the name for the quantity, temperature, i.e. degree Celsius).
e.g.
metre
ampere
litre
kelvin
watt (unit of power)
newton (unit of force)
pascal (unit of pressure)
6.2 Upper and iower case letters for symbols for units
In printed or written material, upright (Roman) letters are used for all SI
symbols.
Examples of the use of symbols are:
Name
Symbol
metre
kilogram
second
ampere
kelvin
watt
newton
pascal
m
kg
s
A
K
W
N
Pa
When symbols are used there is a convention which calls for certain symbols
to be in upper case (capitals).
Generally speaking, the rule is that upper case (capitals) is used only for
the first letter of symbols of unit names related to names of people, most of
them prominent scientists associated with the quantity being measured.
Name
Symbol
Unit named after
ampere
volt
newton
watt
A
V
N
W
(Andre-Marie Ampere - French Scientist)
(Count Volta - Italian physicist)
(Sir Isaac Newton - English mathematician)
(James Watt - Scottish engineer)
6.3 Use of upper and lower case letters for symbols for prefixes
Just as there are rules for the correct use of capital and small letters for the
names and symbols of units, so also there are rules relating to symbols for
prefixes. It is most important that correct usage is made of upper and lower
case letters when we attach symbols for prefixes to3 symbols for units.
The symbols for all prefixes for factors above 10 (k for kilo) are always
in capital letters.
11
Name of prefix
mega
giga
Symbol
M
G
Value
1 000 000.0
1 000 000 000.0
The names of all prefixes unless commencing a sentence are always in
lower case letters,
e.g. milli, kilo, mega, giga.
The following examples will illustrate how important it is to use the correct
symbols:—
Mg=megagram (106 grams) =one million grams
3
=one thousandth part of a gram
but mg=milligram (10~ grams)
IN/IN =meganewton (106 newtons)=one million newtons
3
but mlM=millmewton (10~ newton)=one thousandth part of a newton
6.4 No full stop after symbols, No plural form
Because the symbols are symbols and not abbreviations you must not put
a full stop after them, except at the end of a sentence. Also when dealing with
symbols there is no difference between the singular or plural form.
i.e.
1 metre
=
1 m (not 1 m.)
900 metres
= 900 m (not 900 ms, not 900 ms.)
641 kilograms = 641 kg (not 641 kgs)
Note also that the term SI itself is used in symbolic form and should always
be written SI not S.I.
6.5 Spacing of numerical values and symbolic expressions
When typing, writing or printing SI quantities as symbolic expressions,
always leave a single space between the numerical value and the symbol.
e.g. 107kg
261 N
52m
6.6 Multiplication—combination of symbols for units
When a compound unit is formed by multiplication of two or more units this
may be indicated in one of the following ways (preferably the first).
e.g. metre second can be symbolically written
m.s, nvs, m s
but not ms because ms would mean millisecond.
Likewise, newton metre can be symbolically written N.m, N-m, N m
but not Mm or mN because mN would mean millinewton.
6.7 Division—Combination of Symbols for Units
When a compound unit is formed by dividing one unit by another, this may
be indicated in one of the following ways, e.g. metre per second
—, m/s or by using negative indices m.s~1,
12
likewise kilometre per hour
such expression as k.p.h. must not be used.
Only one solidus (oblique stroke) should be used in a complex unit, for
instance, the unit of acceleration is the unit of velocity (m/s) divided by the
unit of time (s), this can be expressed as
m/s2 or m.s~2 but not m/s/s
In complicated cases, it may be necessary to insert brackets to avoid
ambiguity,
e.g. joule per kilogram per degree Celsius =J/(kg.°C)
6.8 Layout of Numbers
To facilitate the reading of numbers consisting of more than four digits on
either side of the decimal marker, such numbers should be separated into
groups of three dights, counting from the decimal sign toward the left and
the right with a dot on the line used as the decimal marker.
The groups should be separated by a small space but never by a comma.
(this is because the comma is used in Continental Europe to denote the
decimal marker).
Thus an eight figure number which previously you will have recognised
in the form
52,347,941.34
should now be reproduced as follows: —
52 347 941 .34
likewise 52,347.941,34 becomes
52 347.941 34
Note also that the decimal point is in the 'on line' position thus 52 347.941
not 52 347 -941.
6.9 Numbers less than Unity
When writing numbers less than one, a zero must be placed before the decimal
point.
i.e. 0.001 or 0.952
not .001 or .952
7
CONVENTIONS ASSOCIATED WITH THE USE OF SI
7.1 Restricted use of 'centimetre'
As can be seen from
the table of prefixes, SI language prefers multiples of
10 ±1
in stages of 10±3 and although it does provide for the use of 10±2 and
10 , they are only second preference and should be avoided if possible.
The centimetre which has previously been a common metric unit is therefore to be avoided and generally is likely to be used only by the clothing
industry and where directly relating to human dimensions.
*The building and engineering professions and trades have discarded the
use of cent/metre and will use only the millimetre or metre.
13
7.2 Dual Dimensioning not to be used
in the early days of metrication, some non-metric countries thought it wise
in the process of the changeover to use dual dimensions, e.g. 150 mm
(6") longxS'O" (900 mm) high. Whereas the intentions were good the results were disastrous - no one bothered to master the new metric
language or to develop mental concepts of the new metric dimensions. In
addition errors arose from people mixing up the values and the units, e.g.
through error the foregoing example became 150 mm x3 mm high.
It was for this reason that the Royal Observatory in Hong Kong made an
early and fruitful decision to give all weather information in metric units
only; there are other metricating countries which have given weather information in dual language for 1 0 years now and the people of these countries
still speak of temperature in Fahrenheit and rainfall in inches.
It is agreed that the recipient of the information may not immediately
understand the metric values but just as we have grown to accept weather
and sports information in metric units, we will in time become familiar with
metric units in other areas which affect our every day life.
We should therefore avoid the use of dual dimensioning and use only
one language for describing dimensions - metric.
7.3 The hyphen
*
When typing, printing or writing the name of an SI unit never use the hyphen.
If you are running out of space start a new line.
e.g.
always millimetre
7.4 Rounding Off
In the early stages of 'going metric', it will occasionally be necessary to use
conversion tables or conversion factors to make conversions non-metric/
metric or metric/non-metric. A dual language English/Chinese booklet
'Conversion Factors and Conversion Tables' has been published by the
Government Metrication Unit and some common conversion factors are given
at the end of this booklet
Although conversion factors and conversion tables may sometimes be
presented with a large degree of precision, in practice it will seldom be
necessary to present final answers in such precise terms. Each circumstance
will dictate its own requirements but in no case should the final answer
reflect a greater degree of precision than that which was intended in the
original non-metric statement - for instance a requirement may have been
that a photograph size 2" x 2" was to accompany a certain document - by
reference to a conversion table, this would become 50.8x50.8 mm but
clearly 50 x 50 mm would be accurate enough for the intended purposes.
Similarly a sign post could indicate that the distance to the next town is
7 miles and from experience we might know that sign post distances in the
particular district are usually given to the nearest mile. This implies that the
true distance might lie anywhere between 6i and 7J miles. This one mile
range of uncertainty is equivalent to over 1.6 kilometres. Thus it would be
sufficiently accurate to convert the 7 miles to 1 1 kilometres rather than 1 1 .3
kilometres or any more precise figure.
14
7.5 'kilo'—pronunciation
The prefix 'kilo' should be pronounced with the accent on the first syllable
and 'o' pronounced as in 'oh!'. Thus 'kill-oh'. To place the accent on the
'o' or to pronounce the 'o' as in'tot' is incorrect
Correct pronunciation is thus kill-oh-gram, killo-oh-newton and killoh-metre (NOT klaw-gram, klaw-newton, klaw-metre).
7.6 'kilo'—misuse of the term
If you refer back to the list of prefixes, you will see that the prefix 'kilo'
means "x1 000".
Occasionally one finds that people use the term 'kilo' and usually pronounced 'kee-low'; sometimes to mean kilogram, or even to mean kilometre,
sometimes to mean kilowatt. Whereas the text will usually indicate the implied
unit it is nevertheless wrong - 'kilo' used on its own without the name of the
unit attached, can only mean 'multiplied by 1 000' and nothing more. Most
certainly the word 'kilo' on its own, must not be used in written work, always
write kilogram, kilometre, kilowatt and kilonewton.
8
ENGLISH/CHINESE TRANSLATIONS
A booklet entitled English/Chinese Glossary of SI Terminology has been
published by Government Information Services Department.
The booklet sets put the official English/Chinese translations and spellings
of SI units and prefixes and also their symbols.
It should be noted that although the names of units and prefixes bear change
in translation, the symbols are identical whether in English or Chinese text.
For example
English
Chinese
Name of Unit
Symbol
Name of Unit
Symbol
metre
kilogram
degree Celsius
m
kg
°C
3fc
=^^
3SRJS
m
kg
°C
For those officers engaged in issuing public statements or notices, attention is particularly drawn to the Chinese translations for the units metre and
kilogram and their multiples and sub-multiples.
e.g.
millimetre
metre
kilometre
milligram
kilogram
3|^
*
^F*
*^
=f-^
(not
(not
(not
(not
(not
Government officers in the course of their duties must strictly adhere to the
approved translations.
15
9
SPECIAL INSTRUCTIONS FOR SECRETARIES,
STENOGRAPHERS AND TYPISTS
9.1 Capitals
(a) When written in full, the names of ALL units start with a small letter,
except at the beginning of a sentence, when a capital is used in the
ordinary way,
e.g.
The height of this door is 2 metres.
Metre is the name of the SI unit for length.
(b) Symbols for units are written in small letters,
e.g.
Unit name
Unit symbol
metre
gram
second
m
g
s
Exceptions to this rule occur when the unit has been named after a person,
e.g.
(c)
Unit symbol
newton
pascal
volt
ampere
joule
watt
N
Pa
V
A
J
W
Prefixes which are names attached to a unit to indicate a decimal
multiple or sub-multiple of the unit are likewise always written in small
letters,
e.g.
(d)
Unit name
kilo
centi
milii
Similarly the symbols for prefixes for values of 1 000 and under are
always written in small letters,
e.g.
Prefix
Symbol
kilo
centi
milli
k
c
m
The exceptions are those which have a value greater than 1 000 (kilo),
e.g.
Prefix
Symbol
tera
giga
mega
T
G
M
16
(e)
Examples of combinations of units and prefixes are
Unit
millimetre
centimetre
kilogram
kiiovolt
megavolt
megawatt
megagram
gigajoule
Symbol
mm
cm
kg
KV
MV
MW
Mg
GJ
9.2 Spacing
(a) When writing symbols for units having prefixes (e.g. kilopascal or
milligram), no space or dot is left between letters making up the symbol.
e.g.
mm not m.m, kg not k g
(b) When writing a symbol after a number to which it refers, a space is left
between the number and the symbol.
e.g. 455 kHz
22 mg
9.3 Product of Units
Symbols for the product of two units may be written in either of the following ways- m.s; m s (the first is preferable).
9.4 The word 'per'
When the word 'per' forms part of the name of a unit (e.g. metres per second),
and is being expressed in symbolic form then the oblique stroke or solidus
should be used. Such things as k.p.h. for kilometres per hour are NOT
ALLOWABLE.
e.g.
For 25 metres per second write 25 m/s not 25 mps.
For 50 kilometres per hour write 50 km/h not 50 kph.
9.5 Plurals
(a) When written in full, the names of units are made plural when necessary.
Decimal fractions are always singular.
Example: 1.5 grams BUT 0.5 gram
(b) Symbols for units are NEVER made plural.
35 kilometres OR 35 km not 35 kms
9.6 Full Stops
A full stop is NOT used after a symbol except at the end of a sentence.
Example: The field measured 450 m by 265 m.
9.7 The Decimal Point
(a) The decimal point should be placed on the line (as a full stop) position.
Example: 25.4,173.02, 15.459
(b) When writing numbers less than one, a zero must be written before the
decimal point. Example: for writing'point five four'put 0.54
17
9.8 Grouping of numbers
(a) For separating groups of three figures, the comma should not be used.
Instead a space is left.* Write 4720 525 not 4,720,525
(A) Where only four figures are involved, the use of the space marker is
optional, except in tabulation, when the space should always be used.
Write either 6875 OR 6 875
Groups of figures on either side of the decimal point should be separated
by the space, where necessary.
Write 0.528 75 not 0.528,75
* This change has been made in order to avoid confusion, since some European
countries use a comma for the decimal point
9.9 The hyphen
When typing, printing or writing the name of a term in SI units never use a
hyphen. If you are running out of space start a new line.
e.g.
always
never
millimetre
milli-metre
9.10 Squares, cubes etc.
When writing symbols for such units as square metres or cubic centimetres,
the correct method is to write the symbol for the unit, followed by the superior
figure 2 or 3, as appropriate.
Examples: For 11 square metres write 11m 2 (not 11 sq. m)
For 23 cubic centimetres write 23 cm3 (not 23 cu. m)
9.11 The Letter 't' for tonne
The correct symbol for the quantity tonne (1000 kg) is Y; however for some
years to come in order to avoid confusion with the abbreviation for the imperial ton (2240 Ibs) which is also Y then the symbol for tonne may be
written as tonne.
A tonne could also be called a megagram, symbol Mg.
9.12 The Letter 'ell' for litre
On some typewriters there is no difference at all between the lower case 'ell'
and the figure 'one'. Since the former is the recognised symbol for litre, which
is an everyday metric unit, it is preferable to spell the word in full, unless the
typewriter has a special script T. However, the symbol ml for millilitre must
be used, since there is no longer any possible confusion.
9.13 Prefixes
A prefix is attached to a unit to indicate a multiple or submultiple of the unit—
millimetre is one thousandth of a metre
kilometre is one thousand metres
The following table shows the factor by which the prefix multiplies the
unit to which it is attached.
18
Prefix
Symbol
Meaning
exa
peta
tera
E
P
T
G
M
one million million million
one thousand million million
one million million
one thousand million
one million
one thousand
one hundred
giga
mega
kilo
hecto
deca
deci
centi
mill!
micro
nano
pi co
k
h
da
d
c
m
Pn
P
ten
one tenth
one hundredth
one thousandth
one millionth
one thousand millionth
one million millionth
9.14 Shorthand outlines
Stenographers will be required to recognise terms by hearing them spoken,
to have a readily available shorthand outline, to remember and be able to use
quickly the specific SI symbol required and to read and type accurately from
technical manuscripts and typescripts.
Following are some shorthand outlines with the longhand interpretation
of the outline.
metre
kilometre
millimetre
gram
kilogram
milligram
litre
kilolitre
millilitre
tonne
second
hour
candela
pascal
newton
millibar
joule
megajoule
kilowatt
degree
Celsius
9.15
Some everyday metric units
Physical Quantity
Name of Unit
Symbol
length
metre
millimetre
centimetre
kilometre
international nautical mile
(for navigation)
m
mm
cm
km
19
Physical Quantity
Name of Unit
Symbol
mass (commonly called
'weight')
kilogram
gram
tonne
second
minute
hour
day
square metre
square millimetre
square centimetre
hectare
cubic metre
cubic millimetre
cubic centimetre
litre
millilitre
kilolitre
metre per second
kilometre per hour
knot (for navigation)
newton
joule
watt
kilogram per cubic metre
tonne per cubic metre
gram per cubic centimetre
kilogram per litre
pascal
ampere
volt
kg
g
tonne
s
min
h
d2
m
mm22
cm
ha3
m 3
mm
cm3
litre or £
ml
kl
m/s
km/h
hertz
revolution per minute
kelvin
degree Celsius
watts per metre kelvin
Hz
rev/min
K
°C
W/m. K
time interval
area
volume
volume (for fluids only)
velocity and speed
force
energy work
power
density
density (forfuilds only)
pressure, stress
electric current
potential difference,
electromotive force
frequency
temperature
thermal conductivity
10
N
J
W 3
kg/m
t/m3 3
g/cm
kg//
Pa
A
V
OFFICE STATIONERY
10.1 Paper sizes
The International A-series of paper sizes has been widely adopted in Hong
Kong. The base size is AO which is 1 square metre in area.
Typed and printed work will generally be prepared on A4 (210 x 297 mm)
or A5 (148x210 mm) size papers. The size of this booklet is A5.
Letters, specifications, Bills of Quantities, and supporting tender documents
will be usually on A4 size papers.
It is recommended that all drawings be prepared on A-series size paper
which if required can fold down conveniently to A4 size for packing and
postage.
20
METRIC DRAWING PRACTICE—
|
..
)
I
'
5
2°>
f
I
1 570
fc.X AMPLE OP ADDITION
DIMENSIONING
3000
.
« I
" M i .
—
3 970
L 700 L
1
-»J
n1
1
2 100
DIMENSIONING
15 A A O
L 900
i
L500L
•!
5 320 ,6 220. 7 320 ,
*!
ON DRAWINGS
-*!
L~ EXAMPLE OF RUNNING
DIMENSIONING
^
i
300
1000L600L L 600L 900l 1 300L
T
9 720
15 4 4 0
1 1 5
,
^
n
12 020
_j
>1
i
2 400
14 420
SCALE = 1
,520
J5 440
^f
*•
100
12
METRIC KNOWLEDGE—TEST YOURSELF
The following sheets have been designed to test how well you have understood and can put into practice the information which has been given to
you in these metric notes.
Questions have been posed and the correct answers appear in the answer
column opposite the next question. For example, question 1 asks: 'What is
the name of the SI unit for length ?', the answer is 'metre' and this appears
in the answer column opposite question 2.
It is recommended that you place a blank piece of paper over the answer
column, so that you can honestly test for yourself how far you have progressed
in learning the new metric language.
25
METRIC KNOWLEDGE—TEST YOURSELF
Answers
Questions
1
What is the name of the SI base unit for length ?
2
What is the symbol for the SI base unit of length ?
metre
3
What is the name of the SI base unit for mass ?
m
4
What is the symbol for the SI base unit of mass ?
kilogram
5
The name of the base unit for time is the 'second'
what is its symbol ?
kg
6
What is the common metric unit used for
expressing temperature?
7
What is its symbol ?
degree Celsius
8
The prefix 'kilo' means?
°C
9
What is its symbol ?
x1 OOOoMQ 3
10 The prefix 'milli' means?
11
k
What is its symbol ?
1 000
or10- 3
12
13
The prefix 'centi' means?
m
one hundredth
or
What is its symbol ?
or
10-2
14
The prefix for one million is mega, what is its
symbol ?
15
The prefix for one millionth is 'micro', what is its
symbol ?
16
102 can be expanded thus 10x10, expand 103.
17
What
is the name of the prefix which expresses
103?
26
M
10x10x10
Questions
Answers
18 What is its symbol?
kilo
19
Expand 106
k
20
What is the name of the prefix which expresses
10 6 ?
10x10x10x10
x10x10
21
What is the symbol of 106 ?
mega
22
Express one thousand metres using the correct
prefix.
M
23
What is the symbol ?
kilometre
24
Express one thousand grams using symbols.
km
25
Milli is the prefix which means ^ QQQ'
kg
express one thousandth of a metre using prefix.
26
What is its symbol ?
millimetre
27
What does one milligram mean in terms of a
gram?
mm
28
What does one kilogram mean in terms of a
gram?
29
500 grams is_
What is the missing word ?
30
What is the unit of area which will replace the
square yard ?
half
31
What is the unit of area which will replace the
acre?
square metre
32
What is its symbol ?
hectare
33
What is the unit which will be used to replace the
cubic foot or the gallon ?
ha
34
A litre is what fraction of a cubic metre?
litre
35
A millilitre is what fraction of a litre?
1
1 000
.of a kHogram.
27
1 O00 xgram
1 000
grams
Questions
Answers
36
A centimetre is what fraction of a metre ?
1
1 000
37
A square centimetre (cm2) is what fraction of
a square metre ?
1
100
38
A cubic centimetre (cm3) is what fraction of a
cubic metre ?
1
1
1
XX «f /%^\ "~—
100^100~~10 000
39
Is there any difference in volume between a
millititre and a cubic centimetre?
1
_
100x100x100
1
000 000
40
Is there any difference in the value of these two
expressions,
(a) (i)10Mg
(ii) 10mg
(b) What does (I) mean ?
(c) What does (ii) mean ?
No
41
The SI unit of density is kilogram per cubic metre.
Express this in symbol form.
(a) yes
(b) 10 megagrams
(c) 10 milligrams
42
Can you express it using negative indices,
(Don't worry if you can't)
kg/m3
43
The SI symbol for kilogram is kg; would it be
correct to express six kilograms as 6 kgs.
kg.m"3
44
What is the correct symbolic expression for six
kilograms ?
No
45
Is it good practice to speak of six 'kilos' of
sausages or any other foodstuff ?
6kg
46
What is the correct expression ?
No
47
'kilo' means one thousand; one thousand times
one thousand is one million. Would it be correct
therefore to say a kilo kilogram for one million
grams (one thousand kilograms) ?
6 kilograms
48
What is the correct prefix for one million ?
No
28
Questions
Answers
49 What is the correct expression for one thousand
kilograms ?
mega
50 What is the common name for one megagram ?
1 megagram
51
tonne
'pounds per square inch' and 'tons per square
foot' were common expressions for pressure in
the imperial system - what is the SI unit of
pressure ?
52 What is the symbol for pascal ?
pascal
53
Perhaps your car tyres were inflated to 26 Ib/in2
previously. The SI equivalent is 180 thousand
pascals, can you express this less clumsily using
prefixes ?
Pa
54
What is the symbolic expression for 180
kilopascals?
180
kilopascals
55
What position does the decimal point take when
writing a decimal fraction,
(a) above the line
(b) on the line
(c) below the line
180kPa
56
Write in numerical form three hundred and sixtyeight point four five six.
(b) on the line
57
Write in numberical form three hundred and sixtyeight thousand four hundred and fifty-six.
368.456
58
Write in numerical form thirty-six thousand eight
hundred and forty five point six.
368456
59
Write in numerical form three point six eight four
five six.
36 845.6
60
Write in numerical form point three six eight four
five six.
3.684 56
61
Write the SI symbols forthe following metric units
(a) millimetre
(e) kilogram per cubic metre
(b) kilogram
(/) pascal
(c) square metre (g) degree Celsius
(d) litre per
(h) cubic millimetre
second
0.368 456
29
Answers
Questions
62 The unit of energy is the joule, the symbol for
joule is J, write in symbolic form the following:
7.62 kilojouies per kilogram degree Celsius.
(a) mm
(b) kg2
(c) m
(d) f/B
(e) kg/m3
(O Pa
(flO °C 3
(/?) mm
63
Write (or type) a copy of the following numbers
correcting any numbers laid out incorrectly,
(a) 1,452 (6)3240170 (c)7640 (d) .917
(e) .64213
64
Copy the following sentences making the
necessary corrections to the layout of numbers,
punctuation use of upper and lower case
symbols, and give symbols where units have
been written in full.
(a) This sheet of paper has a side measuring 210
milli-metres.
(b) The square of 400 is 1160,000.
(c) The area of a football pitch is 12 000 sq. mtrs.
(d) The density of sand is 1 680 kg. per m3
(e) 5 cubic metres of sand has a mass of 8,400
kgs. when dry.
(/) 8.350 Megapascals is the same as 835.0
kilopascals.
7.62 kJ/(kg.°C)
(a) 1 452
(b) 3240170
(c) 7640
(d) 0.917
(e) 0.64213
Answer to Question No. 64
(a)
(b)
(c)
(d)
(e)
(/)
This sheet of paper has a side measuring 210 mm.
The square of 400 is 160 000.
The area of a football pitch is 12 000 m2.
The density of sand is 1 680 kg/m3.
5 m3 of sand has a mass of 8 400 kg when dry.
8.350 MPa is the same as 8 350 kPa.
How good is your metric knowledge in Chinese language?
Questions
Answers
65
What is the character for metre ?
66
In Chinese what is the written symbol for metre ?
30
Questions
Answers
67
What is the character for millimetre ?
m
68
What is the character for kilometre?
69
What is the written symbol for millimetre?
70
What is the character for kilogram ?
71
What is the symbol for kilogram ?
72
What is the character for gram ?
mm
kg
Some General Questions
Answers
Questions
73
A clenched hand measured across the knuckles
measures about ?
74
A 10 cent coin is what diameter?
100 mm
75
The height of your table or desk is about?
20 mm
76
The normal height of a door knob from floor
level is?
750 mm
77
A 50 cent coin weighs?
1m
78
One litre of water (without the container)
weighs?
5 grams
79
Width of hand with fingers outstretched is
1 kilogram
80
The base section of a telephone set weighs about
200 mm
81
From Star Ferry to Kimberley Road via Nathan
Road is
1 kilogram
From Star Ferry to Boundary Street via Nathan
Road is
1 kilometre
82
4 kilometres
31