Saturday, March 14, 2009



This airport announcement was repeated periodically, as I waited for a recent flight:

[By order of the TSA,] liquids, gels, and/or aerosols weighing three ounces or less may be carried through the screening checkpoint.
Do you see what’s wrong with it?

No, I mean besides the stupidity of the useless restriction, the security theatre.

The three-ounce restriction has nothing to do with weight; it refers to volume. It’s a limit of three fluid ounces, not of 3/16 of a pound. Three fluid ounces of shampoo, toothpaste, and deodorant spray do not weigh three ounces each — they don’t all weigh the same amount at all.

Of course, the confusion comes from our use of the word “ounce” for both. If we measured liquid volume in liters and weight in grams, like the rest of the world, we’d make it a limit of 100 ml, and no one would be confused.

We also wouldn’t have to remember strange and arbitrary groupings: 12 inches in a foot, 3 feet in a yard, 1760 yards in a mile, 16 ounces in a pound, and so on. With metric measurements, it’s easy: multiples of 10; you just move the decimal point.

Why, oh, why can’t we switch to the metric system, like the rest of the world?

Or we could go back to cubits.


TwoPi said...

3 US fluid ounces = 0.0009 cubic cubits (thanks to the built-in unit conversion in the google search engine)

The TSA website cites 3.4 fl oz as the limit, so that's a clean 1/1000 cubic cubit.

Curtis Culver culled a cubic cubit of culinary cucumbers. If Curtis Culver culled a cubic cubit of culinary cucumbers, how many culinary cucumbers did Curtis Culver cull?

TwoPi said...

I missed the obvious implication in that arithmetic: the TSA must be using cubic cubits as their standard unit of mesure. We get these oddball regulations ("no more than 3.4 ounces...") once they translate their elegant measurements into Imperial units.