In MS3p geometries, the default external boundary condition is Neumann, as listed in “Default Boundary Conditions”. The normal component of H vanishes on Neumann boundaries. Other boundary conditions can be applied to the external model surfaces as needed. Any external geometry boundary will be treated with the Neumann boundary condition, unless otherwise specified. All models should have at least one source. The simulation properties can typically be allowed to default, but in some cases it may be beneficial to change the type of linear solver, or, more commonly, to lower the iterative solver convergence tolerance in the case where field anomalies are evident in the result.