Method for determining a master time signal in a vehicle, comprising the steps of: a) receiving at least one first server time signal from a first time server; b) receiving at least one second server time signal from a second time server; c) comparing the first server time signal with the second server time signal in order to determine at least one first time difference; d) storing the first time difference; e) determining the availability of the first server time signal and/or the second server time signal; f) using the stored first time difference in order to determine the master time signal at least when at least one of the server time signals (SZ1; SZ2) is not available, g) storing the, in particular encrypted, master time signal and/or at least one, in particular encrypted, server time signal (SZ1; SZ2) in at least one memory (51; 52; 56), wherein at least the first time server and at least the second time server have associated weights that are used in order to determine the master time signal, the weights being stored, preferably in encrypted form, in a memory, wherein the method further comprises a calibration step in order to determine the weights of at least the first time server and at least the second time server, in which a time signal is received from a backend of the vehicle and is defined as master time signal in the calibration step, the time signal transmitted by the backend of the vehicle being a reliable time signal provided with the highest weight, wherein the calibration step involves the master time signal received from the backend of the vehicle being compared with the first server time signal and the second server time signal and the weights being ascertained on the basis of the time differences, ascertained in the calibration step, of the first server time signal and the second server time signal in relation to the master time signal. a) receiving at least one first server time signal from a first time server; b) receiving at least one second server time signal from a second time server; c) comparing the first server time signal with the second server time signal in order to determine at least one first time difference; d) storing the first time difference; e) determining the availability of the first server time signal and/or the second server time signal; f) using the stored first time difference in order to determine the master time signal at least when at least one of the server time signals (SZ1; SZ2) is not available, g) storing the, in particular encrypted, master time signal and/or at least one, in particular encrypted, server time signal (SZ1; SZ2) in at least one memory (51; 52; 56), wherein at least the first time server and at least the second time server have associated weights that are used in order to determine the master time signal, the weights being stored, preferably in encrypted form, in a memory, wherein the method further comprises a calibration step in order to determine the weights of at least the first time server and at least the second time server, in which a time signal is received from a backend of the vehicle and is defined as master time signal in the calibration step, the time signal transmitted by the backend of the vehicle being a reliable time signal provided with the highest weight, wherein the calibration step involves the master time signal received from the backend of the vehicle being compared with the first server time signal and the second server time signal and the weights being ascertained on the basis of the time differences, ascertained in the calibration step, of the first server time signal and the second server time signal in relation to the master time signal. at least the first time server and at least the second time server have associated weights that are used in order to determine the master time signal, the weights being stored, preferably in encrypted form, in a memory, wherein the method further comprises a calibration step in order to determine the weights of at least the first time server and at least the second time server, in which a time signal is received from a backend of the vehicle and is defined as master time signal in the calibration step, the time signal transmitted by the backend of the vehicle being a reliable time signal provided with the highest weight, wherein the calibration step involves the master time signal received from the backend of the vehicle being compared with the first server time signal and the second server time signal and the weights being ascertained on the basis of the time differences, ascertained in the calibration step, of the first server time signal and the second server time signal in relation to the master time signal.