This applet simulates dynamic light scattering measurements. The light intensity is replaced by the distance of the mouse pointer from a fixed position in the applet. Vary this intensity by jiggling the mouse pointer in the graph to simulate Brownian motion. Notice the rapid decrease in correlation for fast mouse movements (small particles) and the slow decay for slow mouse movements (large particles). This is the same way a DLS machine determines the size of the scatterers in your measurement.
The relationship between the speed of Brownian motion and the size of the particle is given by the Stokes-Einstein equation
Autocorrelation Plotter by Darrick Carter; Copyright 2001, Proteinchemist.com