<p>Duke definitely has +/- system.</p>
<ul>
<li>= letter grade + 0.3 (with the sole exception of A+ = 4.0)</li>
<li>= letter grade - 0.3 (with the sole exception of D- = 1.0)</li>
</ul>
<p>Source: [Calculating</a> Grade Point Average - Office of the University Registrar, Duke University](<a href=“http://registrar.duke.edu/registrar/studentpages/student/gpa.html]Calculating”>http://registrar.duke.edu/registrar/studentpages/student/gpa.html)</p>