1.1 The Greek alphabet
The Greek alphabet is used extensively in Europe and the United States to
denote engineering quantities (see Table 1.1). Each letter can have various
meanings, depending on the context in which it is used.
Table 1.1 The Greek alphabet
Engineers’ Guide to Rotating Equipment
1.2 Units systems
In the United States, the most commonly used system of units in the rotating
equipment industry is the United States Customary System (USCS). The
‘MKS system’ is a metric system still used in some European countries, but
gradually being superseded by the expanded Système International (SI)
The USCS system
Countries outside the USA often refer to this as the ‘inch–pound’ system.
The base units are:
foot (ft) = 12 inches (in)
pound force or thrust (lbf)
degrees Fahrenheit (°F)
The SI system
The strength of the SI system is its coherence. There are four mechanical
and two electrical base units from which all other quantities are derived.
The mechanical ones are:
Temperature: Kelvin (K) or, more commonly, degrees Celsius or
Other units are derived from these: for example the Newton (N) is defined
as N = kg m/s2.
Table 1.1 Cont.
As a rule, prefixes are generally applied to the basic SI unit. The exception
is weight, where the prefix is used with the unit gram (g), rather than the
basic SI unit kilogram (kg). Prefixes are not used for units of angular
measurement (degrees, radians), time (seconds) or temperature (°C or K).
Prefixes are generally chosen in such a way that the numerical value of a
unit lies between 0.1 and 1000 (see Table 1.2). For example