Comment by joebig

Minor physics nitpick in the article "...and a gradually widening conductor lets the inductance increase proportionally with key travel instead of jumping abruptly as the metal traverses the field. As the key is pressed, more of the cone moves into the field produced by the coil, inducing eddy currents in the metal. Following Lenz’s law, those currents oppose the original field, which increases the coil’s effective inductance..."

L, the inductance, is reduced, not increased due to insertion of a conductor, unless the conductor is ferromagnetic. A non-ferromagnetic conductor will expel flux due to generated eddy currents, lowering flux-linkage, therefore L, assuming driving coil current is held at a steady rms magnitude.