The present invention claims dyestuffs of formula, wherein D, R1 to R7 and n are defined as given in claim 1, a process for their preparation and their use. The method includes identifying area information for the electronic device and determining whether the electronic device enters a Point Of Interest, using Access Point information included in the identified area information. A shield wire 16 is disposed around wirings connected to the input of a capacitance detection circuit 30 and is connected to a dc potential of low impedance. The air is compressed, adiabatically heated and directed to a heat exchanger mounted in the rim of, and rotating with the centrifuge.