<p>I've heard some people here talking about it; what's so special about it? How is it used in comparison to the other sections?</p>
<p>It doesn’t count towards your score. It’s a way for CB to “test out” new questions and determine their difficulties. They could be used in future tests.</p>
<p>The experimental (CB calls them equating) sections are (more importantly) used to determine the difficulty of the test, and therefore how to generate the curve. Certain questions on that section are repeated verbatim from previous test dates; how well people do on those questions gives the CB a way to separate test difficulty from student quality …</p>