Book set includes three 8.5" x 11" 80 page, case-bound books. The SD-X Reader allows the user to touch pictures and words on the page to learn more information, hear vocabulary words defined, and interact with activities that reinforce knowledge. Each book has about three hours of audio. Set includes: Space is one of six books in the Encyclopedia Britannica Science Library. It provides an exploration of celestial objects in the solar system, from planets to asteroids to comets, as well as human exploration of the solar system. Earth is one of six books in the Encyclopedia Britannica Science Library. It provides an overview of Earth's geology and history, from the materials that make up the Earth, to its geological processes, to natural disasters such as volcanoes, earthquakes, hurricanes, and tornadoes. Humans is one of six books in the Encyclopedia Britannica Science Library. In picture encyclopedia format, it covers human evolution, the development of human culture, important human inventions, and the human body.