alue (positive <span class="emphasis"><em>difference_from_variance</em></span>)
          or testing for a variance less than a nominal value (negative <span class="emphasis"><em>difference_from_variance</em></span>).
          If the latter, then obviously it is a requirement that <code class="computeroutput"><span class="identifier">variance</span>
          <span class="special">+</span> <span class="identifier">difference_from_variance</span>
          <span class="special">&gt;</span> <span class="numb