Some American colleges and universities do not use the semester as the basis of their academic calendar, but choose to use other academic terms, such as the "quarter" or "trimester" system. Most institutions also give credit for short sessions that occur in the summer or between standard semesters. In these cases, the length of the term is shortened from say 15 weeks (in a semester) to around 10 weeks for a quarter, and to as short as four weeks for shorter sessions. Then to create equity in student hours, adjustments are made either to the length of class time or to the assignment of course credit.