DISTANCE ESTIMATION

A method, apparatus and computer program is described comprising: applying a pulse edge to a resonant circuit comprising an inductive element (for inductively heating a susceptor) and a capacitor, wherein the applied pulse edge induces a pulse response between the capacitor and the inductive element of the resonant circuit, wherein the pulse response has a resonant frequency; determining a period or frequency of the resonant frequency of said pulse response; and converting the determined period or frequency into a distance based, at least in part, on a distance gradient and a first calibration measurement. The distance is based on a separation between the inductive element and the susceptor and the first calibration measurement comprises the separation between the inductive element and the susceptor at a calibration temperature.