The voltage-current method of determination of spark energy is satisfactory and informative. Readings may be taken in a minimum amount of time (after the initial system set up) and give the total electrical energy in the arc stream. It is of no significance whether this energy is later transformed to light, heat or sound because the actual causes of ignition are not confined to any one of these forms. The total useful energy i smeasured in its most basic form. Energy dissipated as heat in the plug shell, center conductor and semi-conductors, if present, is not measured by this method. This means that non-contributing energy is eliminated from the results.