Thanks all. It is amazing how seemingly simple question can end up being so difficult to find a definitive answer for. I still think that 'standard' click steps on adjustable reels should have been abandoned in favor of odd sizes never being a problem. But Americans always like 'convenience before universality' so the marketplace disqualifies my opinion.
I liked the 1947 Popular Mechanis article and others here have contributed well to this quest. Thanks. - David Lyga.