In October 1958, Oliver R. Smoot (future Chairman of the American National Standards Institute) repeatedly laid down on the Harvard Bridge connecting Boston and Cambridge, Massachusetts, so that some of his Lambda Chi Alpha fraternity brothers could measure the entire length of the bridge in relation to his height. At 5 feet 7 inches tall, the bridge was found to be 364.4 “Smoots” long (plus or minus an εar). The prank quickly became the stuff of legend (to this day, graffiti on the bridge still divides it up into Smoot-based sections) until finally, in 2011, the word smoot was added to the American Heritage Dictionary, defined as “a unit of measurement equal to five feet, seven inches.” Ten more equally precise units of measurement, and the stories behind them, are explored here. 

1. BARN

A barn sounds enormous, right? You’d think so, but it’s actually equal to somewhere in the region of 0.000000000000000000000001 square centimeters (10^-24cm²)—which is the approximate size of the cross-section of one uranium nucleus. The name was coined by researchers working on the Manhattan Project at Purdue University in Indiana in the early 1940s, and refers both to the relatively large size of the uranium nucleus compared to other elements, and to the fact that it was the intended target—as in, “you couldn’t hit a barn door”—for the atoms whizzing around in their particle accelerator. As whimsical a name as it might be, however, referring to the uranium cross-section they were aiming for as a barn had the added bonus of allowing the researchers to keep their wartime work a secret.

2. SYDHARB

One sydharb is equivalent to 500,000,000,000 liters, namely the approximate volume of Sydney Harbor. Why would you ever need such an enormous measurement? Well, just like using the relative sizes of countries or regions to compare one against another (as in “Brazil is the same size as five Alaskas”), the volume of Sydney Harbor can be used to give context to otherwise incomprehensibly vast quantities like the annual water consumption of a city or country, the size or impact of a flood, and the capacities of lakes and dams.  In comparison, it takes two full days (49 hours to be precise) for 1 sydharb of water to flow over Niagara Falls.

3. BEARD-SECOND

If a light-year is the distance traveled by light in one year (i.e. approximately 6 trillion miles), then a beard-second is the length that a beard hair grows in one second—or, according to Google’s unit converter, 5 nanometers. 

4. MICKEY

Mickey was a mouse of course, and so is that thing attached to your computer. Used by computer scientists and programmers, 1 mickey is the smallest measurable movement of a computer mouse, typically equal to 1/200th of an inch, or just over 0.1mm. The sensitivity of a computer mouse is likewise measured in mickeys-per-inch, while its speed is measured in mickeys-per-second. 

5. CANDLEPOWER

In the 19th century, long before the candela took over as the standard unit of luminous intensity, the relative luminosity of different types of gas- and oil-powered lamps and lights was measured in comparison to one spermaceti candle weighing one-sixth of a pound (76 grams) and burning at a rate of 120 grains (just under 8 grams) per hour. A candle of this size and burning rate, ultimately, would be said to produce 1 candlepower of light. This standard was first introduced in Great Britain by the Metropolitan Gas Act in 1860 and adopted, with some changes, in 1909 by the U.S., the UK, and France. But as technology progressed, the definition of one candlepower changed several times over the decades, before it was finally replaced altogether by the candela in 1948. In modern terms, one candlepower is equal to 0.981 candelas.

6. MICROFORTNIGHT

The Furlong/Firkin/Fortnight or FFF System is a humorous alternative to more standardized, decimal-based measuring systems like SI and the centimeter-gram-second system. Although FFF isn’t really meant to be used in real-world situations (and is instead intended to show just how impractical older systems can be, as well as to test the conversion skills of math students), some of its measurements have nevertheless slipped into wider use: One microfortnight, equal to 1.2 seconds or 1/1,000,000th of two weeks, for instance, is used in the VMS computer operating system.

7. MILLIHELEN

If Helen of Troy had “the face that launch’d a thousand ships,” then 1 millihelen—following the correct system of prefixes in the SI system—is the precise quantity of beauty required to launch one ship, or 1/1000th the number of ships Helen is said to have launched. Although the term is credited to a number of different writers and journalists, it was probably originally coined by Isaac Asimov

8. SWATH

According to the Oxford English Dictionary, 1 swath is “a measure of grass land [or] a longitudinal division of a field,” equal to the breadth of one sweep of a thresher’s scythe. The term has been in use since medieval times but has seemingly never been standardized, and it’s highly likely there were numerous local variations over the centuries. Nevertheless, according to one 19th century agricultural textbook, a single sweep of a scythe should thresh an area roughly 7 feet long by 14 to 15 inches wide—which would make one swath roughly 8 square feet. 

9. DRAUGHT

As a unit of measurement, draught can be used to refer to the distance a standard bow can shoot an arrow (also called the bow-draught or arrow-shot), or to the quantity of fish taken in by one drawing of a fishing net (which is also called a take). Based on that second definition, in the 19th century one draught was a measurement of eels that came to exactly 20 pounds.

10. MUGGESEGGELE

One Muggeseggele is equal to 0.22mm, or just under 1/100th of an inch. Not the most useful of measurements you might think, but that’s the point: In Swabian German, Muggeseggele is used as a byword for any proverbially tiny distance, length, or measure, like “a hair’s breadth” or “a cat’s whisker” might be used in English. Be careful when you drop this one into everyday conversation, however—Muggeseggele literally means “a house fly’s scrotum.”