The grading system used by the IBO is criterion-referenced. This means that each student's performance is measured against well-defined levels of achievement consistent from one examination session to the next. Each examined subject is graded on a scale of 1 (minimum) to 7 (maximum). The award of the Diploma requires students to meet defined standards and conditions including a minimum total of 24 points and the satisfactory completion of the extended essay, TOK and CAS activities. The maximum score of 45 points includes three bonus points for an exceptional essay and work in TOK. Students who fail to satisfy all requirements or who elect to take fewer than six subjects are awarded a certificate for examinations completed.