grad
The French Revolution's 400 gradians, kept in the standard out of metric loyalty.
One grad is 1/400 of a turn: the gradian, or gon, that French revolutionaries proposed to decimalize even the angle — one hundred to the right angle, like one hundred centimeters to the meter. It survived in surveyors' theodolites, on a key of scientific calculators and, solemnly, in CSS.
Legitimate uses, close to none — and that is what makes it a museum piece on active duty: every browser in the world accepts rotate: 100grad and turns the element an exact quarter turn, in involuntary homage to 1795.
.esquadro {
rotate: 100grad; /* = 90deg */
}