This is a video guide that accompanies Modern Marvels Heavy Metals. I use something like this when I need a break or if I have a sub. There are approximately 40 questions that go in order with the video. Modern Marvels videos can be found on the History Channel or the videos can be purchased online. I found it at this link: http://shop.history.com/detail.php?p=69696&SESSID=cb1c85da432a5b00e63888cfc921c695&v=history It sells for $19.99. These videos are perfect when you have a substitute because the videos last about 45 minutes.