  I give here a detailed user guide for the C++ program SHdecay, which has been
developed for computing the final spectra of stable particles (protons,
photons, LSPs, electrons, neutrinos of the three species and their
antiparticles) arising from the decay of a super-heavy X particle. It allows to
compute in great detail the complete decay cascade for any given decay mode
into particles of the Minimal Supersymmetric Standard Model (MSSM). In
particular, it takes into account all interactions of the MSSM during the
perturbative cascade (including not only QCD, but also the electroweak and 3rd
generation Yukawa interactions), and includes a detailed treatment of the SUSY
decay cascade (for a given set of parameters) and of the non-perturbative
hadronization process. All these features allow us to ensure energy
conservation over the whole cascade up to a numerical accuracy of a few per
mille. Yet, this program also allows to restrict the computation to QCD or
SUSY-QCD frameworks. I detail the input and output files, describe the role of
each part of the program, and include some advice for using it best.
