<p>Since every SAT is different, Collegeboard sets the curve based on how hard or how easy they predict it will be. So for a harder test, they will set the curve to be more lenient, while on an easier test, they will set the curve to be more harsh.</p>
<p>For example, on a harder version of the Critical Reading, 3 wrong may be equal to 790, while on an easier version, 3 wrong may be 760. (making up these numbers)</p>
<p>and FYI: Some people think that this curve is based on actual results, but Collegeboard determines it beforehand so that's not the case.</p>