Karlqvist discovered the phenomenon while designing a ferromagnetic surface layer to the magnetic drum memory for the BESK computer. When designing a magnetic memory store, the ferromagnetic layer must be studied to determine the variation of the magnetic field with permeability, air gap, layer thickness and other influencing factors. The problem is non-linear and extremely difficult to solve. Karlqvist's gap discovery shows that the non-linear problem could be approximated by a linear boundary value for the two-dimensional static field and the one-dimensional transient field. This linear calculation gives a first approximation.