A portable electronic device and an auxiliary device each having an interface allowing the establishment of a communication link between them, at least to be able to transmit data representative of a status information from the auxiliary device to the portable electronic device, and-a method of of establishing a measure of an absolute elapsed time in a listening device. The problem is solved in that the portable electronic device has a timing unit for determining a time interval and a memory for storing data, and wherein the auxiliary device has a master timing unit for providing a signal representative of the present time, and wherein the system is adapted to transfer a signal representative of the present time from the auxiliary device to the portable electronic device and to store it in the memory.