In 1976, I worked on the Metropolitan Opera production of "Aida" (or how ever it is spelled) at the "Wolf trap farm park" in Northern Virginia. The theater had a SkKirpan system that used CRT displays. There was a permanent focus remote backstage that you could bring up the channels using a light stylus and touching that channel on the CRT. When I mentioned that I had never seen one before, The Met crew acted like I was from Mars, and that there were many of them on Broadway. For the time it appeared to be just about the most advanced system I had ever seen. The theater burned down a few years later and when rebuilt, It used a totally different system. ( I don't remember what it was).