The influence of a weak magnetic field (B) on the ion current collected by a spherical electrode is studied by means of the 2v-3d particle in cell code SCEPTIC in the limit of zero Debye length. The ion current dependence on B for low fields, shown to be linear, is compared with analytic expressions valid in the magnetized free-flight limit. In the flow-free regime, expressions for the angular distribution of current at different ion temperatures are provided. The configuration in which the plasma is drifting in the B-direction is investigated as well, and a Mach-probe calibration valid for equal temperature ions and electrons is given.