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,
which is
described in some detail in the Physicist's Desk Reference [4]
(which I will abbreviate as PDR from now on), pp. 4-10. In the SI system
the base, or defined, unitsdefined units, are the meter
(m), the kilogram (kg), the second (s), the kelvin (K), and the ampere (A). The definitions of these units in terms of
fundamental physical processes are given in the PDR. All other units are
derivedderived units. For instance, the SI unit of energy,
the joule (J), is equal to 1 
. The derived
units are also listed in the PDR. 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).