I'm wondering if what Pat Naughtin observed in Australia (and elsewhere) about the success of conversion to the SI depending on whether millimetres or centimetres were used as the conventional"small" submultiple of the metre isn't essentially caused by the lack of proper training combined with conscious or unconscious continued use of Imperial units alongside metric units (by way of dual-marked instruments, for example).
I can understand why the latter might be true given the relative closeness of the inch and the centimetre in length. Perhaps the use of the millimetre more or less forced a real break in the old mindset for those sectors and industries that went that route. I realize Pat has said this in his own way, but I'm wondering if it still isn't possible to succeed in converting people to typically use centimetres rather than millimetres in those sectors where it might make sense if the proper kind of training were provided, dual-marked instruments were forbidden, and other ways were found to foster that "clean break" with Imperial thinking and visualization despite the closeness of inch and centimetre measurements. On the other hand, maybe that game is not worth the candle. It might be that you can really leverage the difference in length between the millimetre and the inch to create that clean break, which in effect is what those industries did that converted from feet and inches to millimetres, and that trying to accomplish the same using centimetres is exponentially harder! I can also see how using millimetres would also force the converted to drop using fractions with metric units, something I see far too much of here in the States (1/3 kg, for example). I'd much rather see folks use millimetres with whole numbers or with decimal fractions that hear stuff like "three and one-half centimetres"! Just some speculation this rainy Sunday morning here in Portland, Oregon ... Ezra
