/span><span class="special">&gt;</span> <span class="special">{</span> <span class="special">};</span>
</pre>
<p>
        Now, we want to be able to convert feet to meters and vice versa. The foot
        is defined as exactly 0.3048 meters, so we can write the following
      </p>
<pre class="programlisting"><span class="identifier">BOOST_UNITS_DEFINE_CONVERSION_FACTOR</span><span class="special">(</span><span class="identifier">foot_base_unit</span><span class="special">,</span> <span class="identifier">m