A device for measuring a flow speed in a travel time ultrasonic flow meter, comprising - a first connector for a first ultrasonic element (11, 22), - a second connector for a second ultrasonic element (13, 23), - a transmitting unit for sending an impulse signal to the first connector, - a D/A converter, the D/A converter being connected to the first connector, - an A/D converter, the A/D converter being connected to the second connector, - a computer readable memory for storing the measuring signal, - a receiving unit for receiving a response signal to the impulse signal from the second connector, characterised in that it comprises: - a selection unit for selecting a portion of the received response signal or a signal derived therefrom, - an inverting unit for inverting the response signal with respect to time to obtain an inverted signal, wherein the inverting unit is provided for inverting the selected portion of the response signal with respect to time to obtain the inverted signal, the inverting of the signal portion comprising reversing the order of recorded samples of the received response signal, - a processing unit (15, 16, 71) for deriving a measuring signal from the inverted signal and storing the measuring signal, the derivation of the measuring signal comprising digitizing the response signal or a signal derived therefrom with respect to amplitude, - a measuring signal generator, the measuring signal generator being connectable to the first connector or to the second connector, - a transmitting means for sending the measuring signal to the first connector, - a receiving unit for receiving a response signal of the measuring signal from the second connector, - a second processing unit (15, 16, 71) for deriving a flow speed from the received response signal. - a first connector for a first ultrasonic element (11, 22), - a second connector for a second ultrasonic element (13, 23), - a transmitting unit for sending an impulse signal to the first connector, - a D/A converter, the D/A converter being connected to the first connector, - an A/D converter, the A/D converter being connected to the second connector, - a computer readable memory for storing the measuring signal, - a receiving unit for receiving a response signal to the impulse signal from the second connector, characterised in that it comprises: - a selection unit for selecting a portion of the received response signal or a signal derived therefrom, - an inverting unit for inverting the response signal with respect to time to obtain an inverted signal, wherein the inverting unit is provided for inverting the selected portion of the response signal with respect to time to obtain the inverted signal, the inverting of the signal portion comprising reversing the order of recorded samples of the received response signal, - a processing unit (15, 16, 71) for deriving a measuring signal from the inverted signal and storing the measuring signal, the derivation of the measuring signal comprising digitizing the response signal or a signal derived therefrom with respect to amplitude, - a measuring signal generator, the measuring signal generator being connectable to the first connector or to the second connector, - a transmitting means for sending the measuring signal to the first connector, - a receiving unit for receiving a response signal of the measuring signal from the second connector, - a second processing unit (15, 16, 71) for deriving a flow speed from the received response signal. - a selection unit for selecting a portion of the received response signal or a signal derived therefrom, - an inverting unit for inverting the response signal with respect to time to obtain an inverted signal, wherein the inverting unit is provided for inverting the selected portion of the response signal with respect to time to obtain the inverted signal, the inverting of the signal portion comprising reversing the order of recorded samples of the received response signal, - a processing unit (15, 16, 71) for deriving a measuring signal from the inverted signal and storing the measuring signal, the derivation of the measuring signal comprising digitizing the response signal or a signal derived therefrom with respect to amplitude, - a measuring signal generator, the measuring signal generator being connectable to the first connector or to the second connector, - a transmitting means for sending the measuring signal to the first connector, - a receiving unit for receiving a response signal of the measuring signal from the second connector, - a second processing unit (15, 16, 71) for deriving a flow speed from the received response signal.