> If we just needed these quantities as the inputs to an equation, sure, we should express them as 1E12 meters or (whatever x 3.6E6) Joules. To be clear, I was

> If we just needed these quantities as the inputs to an equation, sure, we should express them as 1E12 meters or (whatever x 3.6E6) Joules. To be clear, I wasn't advocating against the use of km, cm, kW, etc.; only against the common contrivance that "the cm", "the km", etc. are some sort of independent units with remarkable power-of-ten conversion rules. As an analogy, it's like claiming that the number ½ ("one half") is, coincidentally, the same as the result of "1 ÷ 2" ("one divided by two"). In fact, there is no coincidence; the 'claim' is just describing the intended meaning of the "x over y" notation. Likewise, powers-of-ten are the intended meaning of the "kilo", "centi", etc. notation. In other words, expressing quantities in kilometres is expressing them in metres; there's no need to use, say, scientific notation to make it "more metric". My point about "1000 million kilometres" was simply that it's overly complicated (3 different factors, written in 3 different ways: one with digits, one in English and one as a prefix); why not "1 billion kilometres", "1 trillion metres" or even "1 terametre" ;) The problem with kilowatthours isn't the "kilo" or the "Watt", but the "hours"; it introduces an unnecessary factor of 3600 compared to other units. For example, a megawattsecond (AKA a megajoule) has the same order of magnitude (1kWh = 3.6 MWs)