I was curious about the history and technical evolution of the whelen edge lightbar platform. I know that multiple generations existed from it's inception in 1983 thought to 9M and freedom LED lightbars of the 2000s and 2010s. There isn't a whole lot about it technically like there is for Twinsonic and Aerodynic. Also how can I spot the different generations of them, I can tell an older model from the 80s or 90s from a late 90s or 2000s model but not specifically. What revisions were made and how did the technology change in this long lasting and legendary platform?