What is the Radian? (with Geogebra4.25 in html)

Click on the picture to launch the applet

or

follow this link

http://dmentrard.free.fr/GEOGEBRA/Maths/export4.25/Radiananim.html

here you can see the use of this applet:     http://youtu.be/2bNTr8RXIIQ