== Benefits of SPI ==
Here is a list of the benefits of SPI.<<BR>>
Inside ( ) are alternative techniques.

=== Reduction of the RMS motion of the mirrors ===
 * Easier lock acquisition   (Pre-locking of the arms)
 * Stabler operation         (Hierarchical control)
 * Less up conversion noise  (Hierarchical control)
 * Less laser noise coupling (Hierarchical control)
 * Less actuator noise       (Hierarchical control)

=== Reduction of the seismic noise ===
 * Low frequency seismic noise
 * Vibration introduced from the heat link  (Better heatlink isolation. Local SPI.)