Textbooks in vCalc are opensource textbooks, where the complete text is present with images and connections from chapter to chapter. vCalc's unique contribution is that formula (equation) calculators in the textbook chapters are also present in a set of buttons in each chapter.  You can execute the equation calculators by clicking on the buttons or by clicking on the formulas in the text.  In both cases, a calculator window will popup with that equation pre-programmed. 

Here is an example of a chapter on oscillations from the physic text book, Light and Matter.