If exam grades are posted and one student receives a 71 and another receives a 68 and minimum score required to pass is 70, the student with the 71 keeps the 71.  The 68 students needs to retest.  If the score on the retest is 93, that student does not receive a 93 for the exam grade.  The retest score is always a 70 no matter the retake passing score.  This keeps the retest student from profiting from remembering exam questions from the first exam.  Second chance exams are different from the first exam to ensure subject matter knowledge is tested and not exam question memory skills.