This machine is a sequencing instrument, a Sanger sequencer, which implements a traditional type of sequencing. The plates go in and the machine analyzes the reactions. Each base is represented by a different color. The machine processes the bases, and sorts them, producing this four-color chromatogram. The peaks on the graph correspond to the intensity of color, and translates each color into a letter. By reading left to right, one can see the sequence of the material. A computer compares one viral sequence to another, and determines how closely related different viruses are to one another. This creates a family tree of viruses that allows CDC to visualize how the viruses are moving throughout a country. Reservoirs are then identified, from which the virus spreads. Sequencing gives us a window as to where a virus has been, and how long it has been circulating, allowing CDC to focus its vaccination programs on specific regions inside pertinent countries.