Please allow time for the applet to load. Depending on your connection speed and computer muscle, it could take as long as 5 minutes for all of the applet's sounds and images to load over the network and initialize.
If you don't know what Musical Set Theory is, please read all about it. (Includes help on using the applet.)
If you switch to another window and then come back to this web page, the applet's piano keyboard and clockface map do not redraw. As far as I can tell, this is a Java problem and not my problem. But to facilitate things, I've added a Redraw button on the side bar. Just click redraw after switching windows has erased those parts of the applet.