Elements I is a book app. It is designed for students and teachers. Elements I redesigns the classical geometry book - Euclid's Elements of Geometry (book I) in a new way. With the new technology supporting, it is showing a vivid way to display the great mind contained in Euclid's Elements of Geometry.In this book app, the demonstrations are interactive, that are providing a easy way for you to control the geometry objects, like change the length of a segment, move a point form one place to another and so on. It makes geometry learing interesting.Relationship between geometry objects in the demonstrations will be real show out. Following the radius of a circle changing, the size of this circle will change at the same time.