Handbook for Sound Engineers

Fundamentals and Units of Measurement 1647

48.1 Units of Measurement

Measurements are the method we use to define all
things in life. A dimension is any measurable extent
such as length, thickness, or weight. A measurement
system is any group of related unit names that state the
quantity of properties for the items we see, taste, hear,
smell, or touch.
A unit of measurement is the size of a quantity in the
terms of which that quantity is measured or expressed,
for instance, inches, miles, centimeters, and meters.
The laws of physics, which includes sound, are
defined through dimensional equations that are defined
from their units of measurements of mass, length, and
time. For instance,

where
L is length,
W is width,
D is distance,
T is time.

A physical quantity is specified by a number and a
unit, for instance: 16 ft or 5 m.

48.1.1 SI System

The SI system (from the French Système International
d’Unités) is the accepted international modernized
metric system of measurement. It is used worldwide
with the exception of a few countries including the
United States of America.
The SI system has the following advantages:

1. Internationally accepted.


2. All values, except time, are decimal multiples or
   submultiples of the basic unit.


3. It is easy to use.


4. It is easy to teach.


5. It improves international trade and understanding.


6. It is coherent. All derived units are formed by
   multiplying and dividing other units without intro-
   ducing any numerical conversion factor except one.


7. It is consistent. Each physical quantity has only one
   primary unit associated with it.

When using the SI system, exponents or symbol
prefixes are commonly used. Table 48-1 is a chart of the
accepted name of the number, its exponential form,

symbol, and prefix name. (Note because of their size,

the numbers from sextillion to centillion have not been

shown in numerical form and symbols and prefix names

have not been established for these numbers.)

48.1.2 Fundamental Quantities

There are seven fundamental quantities in physics:

length, mass, time, intensity of electric current, tempera-

ture, luminous intensity, and molecular substance. Two

supplementary quantities are plane angle and solid angle.

Area= L Wu

Velocity D

T

--- -=

Table 48-1. Multiple and Submultiple Prefixes

Name of

Number

Number Exponen-

tial Form

Sym

bol

Prefix

Centillion 1.0 × 10^303

Googol 1.0 × 10^100

Vigintillion 1.0 × 10^63

Novemdecillion 1.0 × 10^60

Octodecillion 1.0 × 10^57

Septendecillion 1.0 × 10^54

Sexdecillion 1.0 × 10^51

Quindecillion 1.0 × 10^48

Quattuordecillion 1.0 × 10^45

Tredecillion 1.0 × 10^42

Duodecillion 1.0 × 10^39

Undecillion 1.0 × 10^36

Decillion 1.0 × 10^33

Nonillion 1.0 × 10^30

Octillion 1.0 × 10^27

Septillion 1.0 × 10^24 EExa-

Sextillion 1.0 × 10^21 P Peta-

Trillion 1,000,000,000,000 1.0 × 10^12 T Tera-

Billion 1,000,000,000 1.0 × 10^9 GGiga-

Million 1,000,000 1.0 × 10^6 M Mega-

Thousand (^1000) 1.0 × 10^3 k Kilo-
Hundred 100 1.0 × 10^2 h Hecto-
Ten 10 1.0 × 10^1 da Deka-
Unit 1 1.0 × 10^0 ——
Tenth 0.10 1.0 × 10–1 d Deci-
Hundredth 0.01 1.0 × 10–2 c Centi-
Thousandth 0.00 1.0 × 10–3 m Milli-
Millionth 0.000 001 1.0 × 10–6 μ Micro-
Billionth 0.000 000 001 1.0 × 10–9 nNano-
Trillionth 0.000 000 000 001 1.0 × 10–12 pPico-
Quadrillionth 0.000 000 000 000 0011.0 × 10–15 f Femto-