  The current methods to determine the primary energy in surface arrays are
different when dealing with hadron or photon initiated showers. In this work,
we adapt a method previously developed for photon-initiated showers to hadron
primaries. We determine the Monte Carlo parametrizations that relate the
surface energy estimator and the maximum of shower development for both, proton
and Iron primaries. Using for each primary their own set of calibration curves,
which is of course impossible in practice, we show that the energy could be
inferred with a negligible bias and 12% resolution. However, we show that a
mixed calibration could also be performed, including both type of primaries,
such that the bias still remains low and the achieved resolution is around 15%.
In addition, the method allows the simultaneous determination of Xmax in pure
surface arrays with resolution better than 7%.
