I actually asked an astronomer once why he would say "approximately 2 light years," when he could've said "approximately 20 petameters" and have it be more universal -- a light year is not a universal measure since different countries use a different length of base time for the year. He said, "Oh, I've never heard anyone use that prefix on meters before."
It's the metric system people, you memorize 10 measures and 15 prefixes and you're good for life as a scientist. English majors only need 7 units and 5 prefixes. Shorter than the alphabet. Why don't they teach this in America schools yet?
And no, memorizing 25.4mm == 1" is not learning the metric system. And no, kids don't actually have to know even that to graduate high school.
I could memorize how many inches in a hand, hands per foot, feet per yard, yards per furlong, furlongs per mile, miles per knot, knots per league, leagues per light second, lights seconds per light minute, light minutes per AU, AUs per light year, and light years per parsec... (hint: none of those are powers of ten). Also, length is measured in inches, but width is measured in gauges?
But that's already as complex as the entire metric system, and I haven't even hit ounces yet! Quick, do I mean volume or weight?