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.