An electrical discharge state detecting device for an electrical discharge machining machine which detects an electrical discharge state during an electrical discharge machining operation. The metal strip is heated and annealed in a heating furnace and subsequently the required strip temperature and surface properties are adjusted in a cooling zone. The first command prepares a data object for a snapshot. The erbium dielectric material and the single crystal dielectric material of the second spacer are substantially crystal lattice matched at the second surface. This makes it possible to precisely detect a boundary position between the data-recorded area and non-recorded area.