  There are many complementing strategies to estimate the extrapolation errors
of a model which was calibrated in least-squares fits. We consider the
Skyrme-Hartree-Fock model for nuclear structure and dynamics and exemplify the
following five strategies: uncertainties from statistical analysis, covariances
between observables, trends of residuals, variation of fit data, dedicated
variation of model parameters. This gives useful insight into the impact of the
key fit data as they are: binding energies, charge r.m.s. radii, and charge
formfactor. Amongst others, we check in particular the predictive value for
observables in the stable nucleus $^{208}$Pb, the super-heavy element
$^{266}$Hs, $r$-process nuclei, and neutron stars.
