Covering a wide historical period from Pythagoras' mathematics of music and colour in ancient Greece, to Castel's ocular harpsichord in the 18th Century, to the visual music of the mid-20th Century, to the liquid light shows of the 1960s, and finally to the virtual reality and projection mapping of present moment, this is both an over-arching history of real-time visuals and audio-visual art, and also a crucial source for understanding the various theories about audio-visual synchronization.