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<h4 class="subsection" id="CGS-Units-Systems-1"><span>8.1.2 CGS Units Systems<a class="copiable-link" href="#CGS-Units-Systems-1"> &para;</a></span></h4>
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<p>The ESU system derives the electromagnetic units from its unit of
charge, the statcoulomb,
which is defined from
Coulomb&rsquo;s law.  The statcoulomb equals
\({{\rm dyne}^{1/2}\,{\rm cm}}\)
 or 
\({{\rm cm}^{3/2}\,{\rm g}^{1/2}\,{\rm s}^{-1}}\)
.
The unit of current, the statampere, is statcoulomb&nbsp;sec<!-- /@w -->, analogous to
the relationship in SI.  Other electrical units are then derived in a
manner similar to that for SI units; the units use the SI names prefixed
by &lsquo;<samp class="samp">stat-</samp>&rsquo;, e.g., &lsquo;<samp class="samp">statvolt</samp>&rsquo; or &lsquo;<samp class="samp">statV</samp>&rsquo;.  The prefix
&lsquo;<samp class="samp">st-</samp>&rsquo; is also recognized (e.g., &lsquo;<samp class="samp">stV</samp>&rsquo;).
</p>
<p>The EMU system derives the electromagnetic units from its unit of current,
the abampere, which is defined in terms of Ampere&rsquo;s law.  The abampere
is equal to
\({{\rm dyne}^{1/2}}\)
 or
\({{\rm cm}^{1/2}{\rm g}^{1/2}{\rm s}^{-1}}\)
.
The unit of charge, the abcoulomb, is
abampere&nbsp;sec<!-- /@w -->, again analogous to the SI relationship.
Other electrical units are then derived in a
manner similar to that for SI units; the units use the SI names prefixed
by &lsquo;<samp class="samp">ab-</samp>&rsquo;, e.g., &lsquo;<samp class="samp">abvolt</samp>&rsquo; or &lsquo;<samp class="samp">abV</samp>&rsquo;.  The magnetic field
units include the gauss, the oersted and the maxwell.
</p>
<p>The Gaussian units system, which was also known as the Symmetric
System,
uses the same charge and current units as the ESU system (e.g.,
&lsquo;<samp class="samp">statC</samp>&rsquo;, &lsquo;<samp class="samp">statA</samp>&rsquo;); it differs by defining the magnetic field
so that it has the same units as the electric field.  The resulting
magnetic field units are the same ones used in the EMU system: the
gauss, the oersted and the maxwell.
</p>
<p>The Heaviside&ndash;Lorentz system appears to lack named units.  We define
five basic units, &lsquo;<samp class="samp">hlu_charge</samp>&rsquo;, &lsquo;<samp class="samp">hlu_current</samp>&rsquo;, &lsquo;<samp class="samp">hlu_volt</samp>&rsquo;, &lsquo;<samp class="samp">hlu_efield</samp>&rsquo; and
&lsquo;<samp class="samp">hlu_bfield</samp>&rsquo; for conversions with this system.  It is important to
remember that with all of the CGS systems, the units may look the same
but mean something different.  The HLU system and Gaussian systems
both measure magnetic field using the same CGS dimensions, but the
amount of magnetic field with the same units is different in the two
systems.
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