code: def _vis_calibrate(self, data, key):
          
          # radiance to reflectance taken as in mipp/xrit/MSG.py
          # again FCI User Guide is not clear on how to do this
  
          sirr = self.nc[
              '/data/{}/measured/channel_effective_solar_irradiance'
              .format(key.name)][...]
  
          # reflectance = radiance / sirr * 100
          data.data[:] /= sirr
          data.data[:] *= 100
docs: VIS channel calibration.