I'm assuming that the first enlarger in this series was the 45M, and of course the last is the 45MXT. Does anyone know the order in which the other ones came out? It would help to determine relative age in eBay auctions. And if you know the year a model was introduced or what new features were on it, that would be valuable too. As I understand it, the things that are new on the 45MXT are the straight lower bellows, which makes lens alignment easier and also permits the use of a turret (supposedly the "t" in 45MXT stands for "turret"), and a neoprene seal which is supposed to help prevent light leaks from the negative stage. Was the model before it the 45MXII? I have seen those for sale used fairly often.