If you are reading this textbook in a web browser using a computer with sufficiently wide monitor, you should see button labeled "Calc" just above the text on the page. Clicking on that button will launch a Geogebra calculator applet in the right margin of the book. If the calculator overlaps the text, click on the "Contents" tab above the navigation panel to hide that panel and provide more space for the text. Click again on the "Calc" button to close the calculator app. (And clicking again on the "Contents" tab will re-open the navigation panel.)