The Bad Astronomer has been experiencing some angst over unit systems.
Almost anyone in a technical profession can provide all sorts of complaints about systems of measurement. (I once put a notice on a lab whiteboard that read, “English units suck.”) To me, the oddest thing about all this is exactly the problem at Phil identified: intuition.
I have no everyday intuition for the metric system. I don’t have a good feel for how hot it is in Celsius; nor can I picture the difference between someone 1.4 m tall and 1.8 m tall. I don’t know how much heft a kilogram has if I pick it up in one hand. I don’t know how fast a moving car goes in kph, and I couldn’t deliver a 10 N push.
But, on the other hand, I have no intuition for English/Imperial/US units in a technical context!
I discovered this while spending a summer working for NASA. The Constellation Program, at the time, was officially on English units of measure, and I realized that I had no idea how big things were or what size forces they were experiencing or anything like that. It was a strange inversion of my everyday experience. But then – having been educated in a wonderfully self-consistent system of units, by professors who had synchronized notations – I encountered the horror of a unit that is the “pound mass.” I can understand the desire to try and match the English unit of mass (slugs) to what we usually experience in terms of force and weight, but the real kicker was that as I dug into the “lbm” I encountered inconsistent definitions of the unit. Ack! I ended up just converting everything I was given to metric, doing all the work I needed to do, and then converting it all to English when I finished.
Things were much better that way. And so one of the first things I did in Matlab at my new job was write a bunch of unit-conversion functions.