Google also provides two software development kits that developers can use to create virtual reality content or adapt their already existing applications to it.<ref>Cardboard. 2015. Google Developers [online]. Available online at: https://developers.google.com/cardboard/ (Retrieved 21 October 2015))</ref>
As of January 2016, more than 5 million Google Cardboard viewers was shipped.<ref>https://googleblog.blogspot.cz/2016/01/unfolding-virtual-journey-cardboard.html</ref>
== Main characteristics ==