per minute conversion of the transport propel signal into a target track motor velocity may be accomplished by the propel control 90 itself or preferably by the computer 182 the computer 182 typically compares the left and right track motor sense signals respectively produced by the left and right ppu sensors 198 and 192 to the target track motor propulsion level represented by the transport propel signal the computer 182 communicates the appropriate pump control signals to the left and right track pumps 38 and 40 in response to the outcome of the comparison to compensate for any deviation between the actual and target track motor propulsion levels a display 73 is coupled to the computer 182 or alternatively to the main control unit 250 and preferably communicates messages indicative of operating status diagnostic calibration fault safety and other related information to an operator the display 73 provides quick accurate and easy to understand information to an operator by virtue of the interpretive power of the computer 182 which acquires and processes data from a plurality of track trencher sensors and various geological and geophysical instruments geologic imaging data and related geophysical information for example is visually displayed on the display 73 further information regarding the position of the excavator as it traverses along a predetermined excavation route as well as signal quality information received from the geographic positioning unit 254 is displayed on the display 73 a keyboard 75 is also provided on the main user interface 101 to permit an operator to communicate with the excavator control unit 255 and the main control unit 250 turning now to fig9 there.