thank you for this effort. If possible, I would like the following changs to be made:
1. Simply indicate the speed of light of both media on the left, instead of the complicated formula n1/sin...: the slider[b]s[/b] should vary, let us say between 50 million m/s and 299 792 758 m/s (by definition the max in vacuum!!!)- it would be nice that this number appears as maximum.
In this way both directions can be simulated.

2. Is it possible to drag the two points to other places as well??

3. Other question: do you know of a tool that can be superimposed on the computerscreen and that acts as an meter of the angle between two lines? I would need it to determine angles of forces that act given photo's or certain daily live situations. It should be possible to make it pop up, drag it to a certain place on the screen, and to point one leg in one direction, the other in another direction, and the angle between both legs appears. You understand that I could also use this in the optics simulation (later, after the sine function is known)

Thank you very much!
I hope you had a good time in Troya hotel, with all the water melon!

Wim  (PS Not Vim :-)  )