6Prof. Richard Pogge. How I Compute Your Course Grade: A Worked Example [EB/OL]. http://www. astronomy.ohiostate.edu/- pogge/Ast161/Quizzes/grade. html. 2009-4- /2009, 4-20.
7Prof. Richard Pogge. In-Class Quizzes, Study Guides & Results [EB/OL]. http://www. astronomy.ohio-state.edu/- pogge/ Ast161/Quizzes/index. html. 2009,4-25/2009-4-25.