A calculating method and a radio system comprising a set of emitters and a set of receivers and a measuring mechanism, which measure the time difference between the reception moments of signals transmitted by the transmitters while the receiver is receiving signals, and which calculate the geometrical time difference of the signals transmitted by the transmitters. The radio system includes a calculating mechanism, which forms the real time difference between the transmission moments of the signals transmitted by the transmitters as a function of time by of measuring the time difference of the signals transmitted by the transmitters as a function of time by of measuring the time difference of the signals received by the receiver and by of the geometrical time difference.