span class="r-in"><span><span class="co"># 4) See the computed scale (pixels per cm)</span></span></span>
<span class="r-in"><span><span class="fu">calibrate</span><span class="op">(</span><span class="va">img</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># scale ~118</span></span></span>
<span class="r-in"><span><span class="co"># 118 * 2.54 ~300 DPI</span></span></span>
<span class="r-in"><span><span class="op">}</span></spa