An optical recording medium has a substrate, and a recording layer formed thereon which contains at least one formazan chelate compound of formula, or . Thus, the inventive method provides to a third party potential customer access to the electronic document authoring, development and distribution system without risking the abuse of the system by the potential customer. The beverage cup may vary in size, shape, and color. On operation of the magnetic field sensor, a current is temporarily applied to the excitation coil in order to bring the ferromagnetic core into a state of predetermined magnetization in which the magnetization of the ferromagnetic core produces no signal in the read-out sensor.