They might not know the conversion factor off the top of their heads, but I think all Americans know or should know what the SI system is.
Just a little response here, because it immediately rang a bell with me when I read Lois's line about the metric system. It might just be a French thing (or okay, it might just be a Kaethel thing
), but when you're grumpy about being somewhere when you'd rather be anywhere else (like Lois is in this case), you sometimes don't want to make the effort to understand things that are not entirely familiar to you. I've been guilty of such behaviour myself a few times (though not about foreign countries, but in contexts that could be compared), and even if it's not the right position to adopt, I imagine that Lois's grunt about the "KM" sign was more a conscious decision to purposefully not understand than true ignorance of what it stands for. Just mho, and I could be way off base, but it's the way I interpreted her line.
Like you say, Laura, it's doubtful that Lois would have no knowledge at all of the metric system.
Kaethel
