  We present analysis techniques to improve the energy resolution of
stereoscopic systems of imaging atmospheric Cherenkov telescopes, using the
HEGRA telescope system as an example. The techniques include (i) the
determination of the height of the shower maximum, which is then taken into
account in the energy determination, and (ii) the determination of the location
of the shower core with the additional constraint that the direction of the
gamma rays is known a priori. This constraint can be applied for gamma-ray
point sources, and results in a significant improvement in the localization of
the shower core, which translates into better energy resolution. Combining both
techniques, the HEGRA telescopes reach an energy resolution between 9% and 12%,
over the entire energy range from 1 TeV to almost 100 TeV. Options for further
improvements of the energy resolution are discussed.
