  The uncertainties on the absolute energy scale of the CELESTE experiment
affect the constraints CELESTE can impose on > 30 GeV gamma-ray emission
models. To date, these uncertainties have been of order 30 %. The optical
throughputs of the atmosphere and the detector are key to understanding the
energy scale. We are comparing CELESTE photomultiplier anode currents measured
for bright stars with predictions from the detector simulation. In these
studies we include data from recently installed radiometers, and from the LIDAR
operating on the site.
