US Patent 9785231 Head worn display integrity monitor system and methods

A head worn display system (e.g., helmet mounted (HMD) display system, and an eye wear mounted display system,) can include a combiner, a head position sensor and a computer. The computer provides symbology in response to first sensor input values associated with the head position. The symbology can be conformal with a real world scene. A monitoring system includes a redundant head position sensor for providing second sensor input values associated with head position. The computer monitors for positional accuracy of the symbology by comparing symbology calculated using the first and second input sensor values or by using an inverse function to compare sensor values.