Day to day we don’t have much to do with words like “cubit,” and some are of purely historical interest — if that. In this country we of course use both conventional measure (feet and inches, pounds and ounces, feet, yards and miles) and the metric system, which was created in the late 18th century in an early and ongoing attempt to create clarity and exactness. As the result of an effort to convert the U.S. to the metric system that stalled in the 1980s, we now buy, for example, gallons of gas and water and quarts of milk, but liters of liquor and Pepsi, which we heat or cool in Fahrenheit (not centigrade) degrees.
This use of different measurement words can be annoying and confusing: It can moreover be very expensive. In 1999 the Mars Climate Orbiter was lost at a cost of at least $125 million because of a “metric mix-up.” To the chagrin and embarrassment of all concerned, the on-board computer had been programmed to use metric data (newton-seconds), but was sent information in customary English units (pound-seconds).
The customary unit “knot” is a good example of the antiquity of some current words of measure. It dates from the 16th century, when sailors threw a log and knotted line into the sea to see how fast the ship was going. It is still used to indicate the speed not only of boats, but also of planes. The knot can further confuse since it is a statement of speed — not distance — equal to one nautical mile per hour. Landlubbers have been know to say things like “that boat goes 10 knots an hour,” which makes the seaman shudder.
The “league” is still heard from, if not used. It was originally about three miles — because a cannon could throw a ball about that far to defend territorial waters. Even now, Good King Wenceslas of Christmas-carol fame discovers that “yonder peasant ... lives a good league hence, underneath the mountain.” The king and the unfortunate page had to walk, depending on local usage, from 2.4 to 4.6 miles, carrying all those pine logs and whatnot.