Abstract: A railroad measuring, gauging, and spiking apparatus uses a closed servoloop arrangement to provide accurate rail gauging. An LVDT sensing arrangement uses three rail feeler wheels to sense the rail gauge immediately adjacent to spiking guns on the apparatus. The output from the LVDT sensor is fed into a signal processing circuit which compares this signal with the desired track gauge in addition to calibrating various analog signals. A gauger control circuit comprises a microprocessor chip which raises and lowers a gauger mechanism and causes the gauger mechanism to track an error signal output by the signal processing circuit until the error signal is equal to zero. The hammers of the spiking guns are interlocked to receive an OK TO SPIKE signal from the microprocessor such that the spiking can not take place until the circuits indicate that the rails are properly gauged.