  The uncertainties involved in the calculation of bottom quark cross-sections
in deep-inelastic scattering at HERA are studied in different phase space
regions. Besides the inclusive bottom quark cross-section, definitions closer
to the detector acceptance requiring at least one high energetic muon from the
semi-leptonic \bquark decay or a jet with high transverse energy are
investigated. For each case the uncertainties due to the choice of the
renormalisation and factorisation scale as well as the \bquark mass are
estimated in the perturbative NLO QCD calculation and furthermore uncertainties
in the fragmenation of the bottom quark to a B-meson and in its semi-leptonic
decay are discussed.
