We examine 33 bow shock crossings by IMP8 and compare different methods to calculate the bow shock normal direction and speed using single spacecraft measurements. We find that the mixed equation by Abraham-Shrauner
combined with the mass flux conservation equation and the minimum-variance technique applied to a limited set of the Rankine-Hugoniot conservation equations give very similar results that are in good agreement with theoretical predictions. The solutions obtained by the velocity coplanarity theorem are reliable only for nearly
perpendicular shocks, while poor results are obtained for such cases from the magnetic coplanarity theorem. We also suggest that in some cases the time resolution of plasma measurements (about 60 s) may be too low to resolve the density behaviour close to the bow shock and to allow definite evaluation of the shock parameters
