Visitors play tones clockwise around this 12-key circle, trying to find the highest note. But although the keyboard appears to play an endlessly rising scale, it is actually only a single set of 12 tones. Each tune is a chord, comprised of six notes of the same pitch, but from six different octaves. One of the notes is louder than the others. Because of this volume shift, the visitor interprets the sounds as an ascending scale, a phenomenon known as the Shepard Scale.