1. In a head worn display system comprising a display, a first head position sensor for providing a plurality of first sensor input values and a computer, the display comprising a combiner, the computer comprising a display generation processor and a display monitor processor, the display generation processor causes a plurality of display symbology to be displayed on the combiner in response to the first sensor input values associated with head position, the display symbology being conformal with a real world scene and being located at a plurality of first symbology positions on the combiner, a monitoring system comprising: the display monitor processor, wherein the display monitor processor is independent of the display generation processor, the display monitor processor calculating a plurality of second symbology positions associated with locations on the combiner calculated in response to a plurality of second sensor input values; and a redundant head position sensor for providing the second sensor input values associated with the head position, the redundant head position sensor being a separate device from the first head position sensor, wherein a comparator of the computer compares the first symbology positions of the display symbology calculated using first independent hardware components of the display generation processor responding to the first sensor input values with the second symbology positions associated with the locations on the combiner calculated using second independent hardware components of the display monitor processor responding to the second sensor input values to determine if the first symbology positions and the second symbology positions are within a tolerance, and the comparator disabling the display of the display if the first symbology positions and the second symbology positions are not within the tolerance.