Precision Luminosity for Z0 Lineshape Measurements with                        
a Silicon-Tungsten Calorimeter                                                 
  
The measurement of the luminosity at the OPAL interaction point is             
based on a Silicon-Tungsten Luminometer, which detects electrons from          
small-angle Bhabha scattering at angles between 25 and 58 mrad.  The           
trajectories of incoming 45 GeV electrons or photons can be determined         
with a total systematic error of less than 7 microns.  The total               
systematic measurement uncertainty on the luminosity is 3.4 10^-4,             
significantly below the theoretical error of 5.4 10^-4.  Such precise          
measurement of the luminosity is crucial for determining the coupling          
of the Z-boson to invisible channels, such as neutrinos.                       
  
 Parallel session :5                   
 Plenary  session :6a