No need to apologize. I was just responding (impersonally) to a position that I thought missed the point concerning what is 'essential' in a technology (the DC-4), and what is not. It was a philosophical point, but an important one, I think, in analyzing or deconstructing anything... you know, the question of what are we really looking at... what is the 'essence' of the objects we are studying. When I think a proponent of a premise is 'missing the point', I, by training, tend to overreact, and for that, I apologize to you for my over-aggressive tone in responding.