rst argument must be a <span class="underline"><code class="computeroutput"><a class="link" href="../boost/units/base_unit.html" title="Class template base_unit">base_unit</a></code></span>.
        The second argument can be either a <span class="underline"><code class="computeroutput"><a class="link" href="../boost/units/base_unit.html" title="Class template base_unit">base_unit</a></code></span> or a <span class="underline"><code class="computeroutput"><a class="link" href="../boost/units/unit.html" titl