A wire on a plane is a common transmission line. One place it is used is as a modification to an existing circuit board. In some cases, one may only be interested in the inductance. The inductance calculated in this tool is the inductance of the loop created by the wire and its return path on the ground plane. It is important to note that this is not the self-inductance of the wire, but rather the closed loop. Inductance gives one an idea of the amount of energy that can be stored in a magnetic field. The only variables used in this calculation are the height of the wire from the reference plane, the radius of the wire, and the relative permeability of the medium surrounding the wire. For all practical purposes, air has a permeability of 1. A vacuum has a permeability of exactly 1.