discussed of course thumbwheel switches 68 may be replaced by a computer generated entry from cpu 42 in the event the data stored in the new sample register 54 is greater than the threshold setting set by the thumbwheel switches 68 a signal occurs on line 70 thus signalling a detected discontinuity the data is fed to the cpu 42 for processing in parallel with the input of the new sample register 54 is a conventional serial memory 72 which feeds data relating to each sample interval to an output register 74 control logic 88 generates a shift signal to the output register 74 upon the occurrence of an output along transfer data output line 76 the location register 78 receives an input from a speed and distance unit 80 such as the type of instrumentation disclosed in the previously mentioned u s pat no 3 864 731 or a milepost detection at input line 82 milepost detection is conventional in track data recording as explained in the previously mentioned u s pat no 3 864 731 of course milepost data may be manually entered by an operator the purpose of the control logic 88 is to permit the passage of data from the serial memory and data regarding speed distance and milepost number to the output register 74 which will then transfer this data upon an enable pulse on line 76 to the cpu 42 thus discontinuity data as well as location data may be processed by the cpu in typical operation of the system shown in fig9 data is taken from the serial memory 72 one word at.