a method of defining the emission coefficient of a surface to be heated by measuring the temperature of a heating surface and the flow of heat from the heating surface to a surface to be heated to derive a pair of values representative thereof and of selecting a previously stored reference emission coefficient from a plurality thereof as a function of the pair of values application_number US 31186505 A description the only drawing represents a self contained cooking field it is provided with a cooking surface 1 at cooking position 2 being formed for instance of a ceramic glass compound below the cooking position 2 there is provided a radiation heat source 4 constituted by an electric radiation heater the emission coefficient of the heat source is designated u03b5 1 and the radiation heat source 4 is insulated from its surroundings by a radiator insulation 6 such that only a small amount of the heat generated by the radiation heater 4 is emitted to the surroundings as lost heat by for the greater amount of the heat generated is radiated from the heating surface a 1 of the radiation heater 4 in the direction of the lower surface of the cooking position 2 during a cooking operation the bottom 10 of a cooking vessel or pot 8 is placed upon the cooking.