Still, even if this is overcome, there will have to be a leap forward in wearable computer technology as well. During the past few years, more convenient brick-size, wearable PCs have been marketed by a number of small firms. The most prominent is Xybernaut Corp., which is selling the U.S. version of Hitachi's Wearable Internet Appliance, known as the Poma -- the first wearable computer to be sold to businesses and consumers through office supply stores and electronics retailers. Essentially a Pocket PC with a color head-worn (single-eye) display, it bears the slim profile of what researchers envision will characterize an AR appliance of the future. But despite its tricked-out design, this device is only as powerful as a typical PDA and far too limited for stereoscopic 3-D position-sensitive AR. The top AR researchers -- Steven Feiner, the developer of MARS at Columbia, and his counterparts at the University of North Carolina, Georgia Tech, and the University of Washington, along with researchers at companies such as Sony and Siemens -- estimate that it will take at least two more years before an AR-capable wearable computer will be developed.