This is a short derivation of the Rogowski equation written with my colleague Dr. Kartikeya Tripathi back in 2010. The first time a new user observes the remarkable properties of the Rogowski geometry (first published by Rogowski and Steinhaus in 1912) to create a current measuring aperture with a flat spatial response and also to reject stray magnetic fields form non-threading currents it looks magical. Like all things magical, it is not. [read full article]