Before proceeding further with dimensional considerations we first need to
discuss units of measurement. In this course we will adopt the SI system of
units (1), which is
described in some detail in the Physics Quick Reference Guide [4]
(which I will abbreviate as PQRG from now on), pp. 4-10. In the SI system
the base, or defined, units, are the meter
(m), the kilogram (kg), the second (s), the kelvin (K), and the ampere (A).(2) The definitions of these units in terms of
fundamental physical processes are given in the PQRG. All other units are
derived. For instance, the SI unit of energy,
the joule (J), is equal to 1 kg m2/s2. The derived
units are also listed in the PQRG. The SI system is referred to as a LMT-class, since the defined units are length L, mass M, and time T (if
we add thermal and electrical phenomena, then we have a 
- class
in the SI system).
Footnotes:
(1) In some older texts this is referred to as the MKS system.
(2) We should also add the mole (mol) and the candela (cd), but these will seldom enter into our models.