It took until the early 1990s before the term ‘augmented reality’ was coined by Caudell and Mizell , scientists at Boeing Corporation who were developing an experimental AR system to help workers put together wiring harnesses. True mobile AR was still out of reach, but a few years later developed a GPS-based outdoor system that presents navigational assistance to the visually impaired with spatial audio overlays. Soon computing and tracking devices became sufficiently powerful and small enough to support graphical overlay in mobile settings. Feiner et al. created an early prototype of a mobile AR system (MARS) that registers 3D graphical tour guide information with buildings and artefacts the visitor sees.