The design of a digibook is: a tree-indexed format in which you opens pages.
On a page text, explanation, assignments and links to VUStat apps occur.
On-top texts
A statistical app usually has an "on-top" text with instructions, commands and answers.
An on-top text allows you to drag, decrease, close, and retrieve with the button 
On some tablets, it is sometimes difficult to maneuver the on-top.
One reason is usually that your fingers are somewhat dry, a little damping helps.
Navigate
If you start an app from a page of the digibook, you'll see two tabs.
One tab "The TITANIC, ..." and a tab of an app, eg "Data Analysis".
You can switch between page and app through the tabs.
If you finish an assignment, close the app. That prevents you from having a whole zipper of tabs open.
The VUStat apps
You can of course also start the VUStat apps on their own.
The link is www.vustat.eu
The menu of an app opens with the button 
