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      <title>Form effect</title>
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      <div class="title_topic2" id="xps10_pagetitle">Form effect</div>
      <hr noshade="true">
      <p class="para_topic">The form effect examples demonstrate the effects that form tolerances have on the variation calculated by Tolerance Stackup Validation.</p>
      <div class="title_division">Case 1</div>
      <p class="para_division">A simple block (2.0 inches on each side) has two tolerances, as shown in the figure below:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">The left face of the block is considered a datum (Datum A) and has a form tolerance (a flatness of 0.050).</p>
         </li>
         <li>
            <p class="para_item">The opposite face, the right face, has a directed dimension of 2.0+/-0.005. The origin of this dimension is Datum A.</p>
         </li>
      </ol>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/qs_form_case1.gif"></p>
      </div>
      <div class="title_figure">Block with two tolerances</div>
      <p class="para_division">After running a Tolerance Stackup Validation analysis, this is the summary in the Information window:</p>
      <p align="center"><img align="bottom" src="graphics/qs_form1_info.gif"></p>
      <p class="para_division">The total calculated variation between the two faces is 0.06, as both the form and directed dimension contribute to the total variation. The specified measurement simulates the measurement taken by a caliper between two points (in this case, the center point of the left and right faces).</p>
      <p class="para_division">The form effect (the flatness tolerance of 0.050 on the left face) plays inside the box volume. This leads to a minimum variation of 1.9450 (2.0 - 0.05 - 0.005), and a maximum variation of 2.0050 (2.0 + 0.005).</p>
      <div class="title_division">Case 2</div>
      <p class="para_division">This example is the same as Case 1, except a flatness tolerance has been added to the right side. The tolerances for Case 2 are:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">The left face of the block is considered a datum (Datum A) and has a form tolerance (a flatness of 0.050).</p>
         </li>
         <li>
            <p class="para_item">The opposite face, the right face, has a directed dimension of 2.0+/-0.005. The origin of this dimension is Datum A.</p>
         </li>
         <li>
            <p class="para_item">A flatness tolerance (0.003) is specified for the right face.</p>
         </li>
      </ol>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/qs_form_case2.gif"></p>
      </div>
      <div class="title_figure">Block with three tolerances</div>
      <p class="para_division">After running a Tolerance Stackup Validation analysis, this is the summary in the Information window:</p>
      <p align="center"><img align="bottom" src="graphics/qs_form2_info.gif"></p>
      <p class="para_division">The total calculated variation between the two faces is 0.06, as in Case 1. The flatness of 0.003 on the right face is a refinement of the directed dimension, and therefore its effect cannot be seen in the calculated variation.</p>
      <div class="title_division">Case 3</div>
      <p class="para_division">The box from Case 1 (with two tolerances) is put on top of a plate simulating a gauge fixture.</p>
      <div class="figure">
         <p align="center"><img align="bottom" src="graphics/qs_form_case3.gif"></p>
      </div>
      <div class="title_figure">Block and plate</div>
      <p class="para_division">This is the final configuration of the two components. In a metrology cell to measure the height of the box, the operator has two choices:</p>
      <ol type="1" start="1">
         <li>
            <p class="para_item">Use a caliper, measuring point to point, as in Case 1.</p>
         </li>
         <li>
            <p class="para_item">Use a calibrated plate to use as origin for the measurement (this case). F1 and F2 are the faces selected for the measurement.</p>
         </li>
      </ol>
      <p align="center"><img align="bottom" src="graphics/qs_form3_meas.gif"></p>
      <p class="para_division">After the Tolerance Stackup Validation analysis has calculated the variation between F1 and F2, the results in the Information window are:</p>
      <p align="center"><img align="bottom" src="graphics/qs_form3_info.gif"></p>
      <p class="para_division">In this case, the total variation is 0.01, because there is only the contribution of the directed dimension. There is no effect from the form (the flatness tolerance), because the box is mating with the fixture on the high points of the plane (Datum A). This means that the form effect does not appear in the final calculation.</p>
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