Online - Offline usage

An internet connection is required to download the ebooks. The size of an ebook is about 50MB. In addition to the installation of the ebooks, data is also needed for playing the videos. However these can also be saved beforehand locally (via media). 

The formula editor is still finds itself at an experimental stage and requires an internet connection for the displaying and creation of formulas. 

The actual reading and modification of the ebook otherwise needs no data connection!