Abstract: The invention relates to a mobile data recording medium, in particular a data card, comprising a memory field having a number of bits which can be read, cleared and reloaded by means of a data exchange device, wherein the memory field includes a first memory region having a number of memory locations, each having at least a bit, each bit representing a value unit and each memory location representing a predetermined time interval, and that the memory field includes a second memory region having a plurality of bits which second memory region represents a time period predetermined by its beginning and its length, wherein the length of the time period is a multiple of said predetermined time interval.