>=</mo>
                    <mi mathvariant="italic">radius</mi>
                </mrow>
            </math>
            (<span class="emphasis"><em>t</em></span> increases linearly along longitudinal
            lines),
            and <span class="emphasis"><em>s</em></span> ranges from 0.0 at the +<span class="emphasis"><em>y</em></span> axis, to 0.25 at the
            +<span class="emphasis"><em>x</em></span> axis,
            to 0.5 at the \-<span class="emphasis"><em>y</em></span> axis, to 0.75 at th