Zannos, Susan. Charles Richter and the Story of the Richter Scale (Unlocking the Secret of Science) (2003). This biography and science series profiles achievers in science and their historical contribution in science. Charles Richter is recognized as developing the "magnitude scale" later changed to richter scale because he formulated a way to evaluate the intensity of an earthquake. The seismologist machine provides a visual reading P waves and S waves, which Charles Richter used to calculate between each one and find the actual earthquake intensity. It replaced the old scale called Mercalli Scale. The mercalli scale was used to determine the intensity of earthquakes but it proved to be inefficient and not practical. This science series also includes the history of major earthquakes and further explains the tectonic plates and faults as the cause of earthquakes. I recommend this science series for its easy reading and succinct information. Target Audience: Middle School (Science Series).