An audio system includes a first transformation device provided with an input audio signal and which transforms the input audio signal from the time domain to the frequency domain resulting in an input spectrum. The invention is based on the idea that generation of random number data and the calculation of digital signatures are performed before information data is accessible to a digital pen. The outlet end or needle hub of a syringe or insulin pen fits in the flange, with the syringe needle extending through the orifice, thereby securing the disk to the syringe. A locking mechanism may be included to keep the flag in position relative to the supporting base or label. In a preferred embodiment, the radiation source\u2014which is, for example, a superluminescent light emitting diode\u2014and the bandpass radiation filter are provided on a common mount which is in contact with a thermoelectric cooler acting, together with temperature sensing means and control means, as temperature stabilizer. The invention also relates to a surge arrester arrangement, to a use of an electrical insulator for insulating a surge arrester, and to a method for production of such an electrical insulator.