# Measure for measure from an attoparsec to the jerk

When you use as part of your daily work a unit of measure that Wired magazine lists as among the Best Obscure Units, you know you are in trouble. Thus I found pack-year, one of an epidemiologist’s favorite smoking exposure measures listed there along with a couple of other units I knew about. Pack-years is a cumulative measure calculated by multiplying the number of packs of cigarettes a person smoked per day by the number of years they smoked them. Thus a 25 pack-year smoking history can be accrued by smoking a pack a day for 25 years, or, heaven forbid, 25 packs a day for one year. Obviously this measure has to be used carefully with diseases that take time to develop (latency), but that’s what epidemiologists get paid the big bucks for.

A couple of other units on the short Wired list I also knew about, like a unit of length, the smoot. Oliver R. Smoot was an MIT undergraduate whose frat house was across the Harvard Bridge spanning the Charles River between MIT and Boston (I know it should be called the MIT Bridge, but it isn’t). His fraternity brothers had the idea of measuring the bridge in smoots and you can still see Mr. Smoots’s unit length painted, seriatum, on the bridge (it’s been many decades but the markings keep reappearing). A couple of others I didn’t know about: the gou (180 milliliters — better known as a rice cup for an electric cooker), the thrave (24 sheaves of wheat), the shake (10 nanoseconds), the mickey (ratio of computer mouse movement to onscreen cursor movement), the jansky (strength of radio signals from space).

There are undoubtedly lots of useful measures not commonly used and I found some in Wikipedia. Here are some I found interesting (what does this say about me, I wonder?). Check the Wikipedia entry for more and the cites, which I have omitted:

Attoparsec
Parsecs are used in astronomy to measure enormous interstellar distances. A parsec is approximately 3.26 light-years or about 3.085×1016 m. Combining it with the “atto-” prefix yields attoparsec, a conveniently human-scaled unit of about 3.085 centimeters (about 1-7/32 inches) that has no obvious practical use but does have a proper SI symbol, apc. Interestingly, 1 attoparsec/microfortnight is nearly 1 inch/second (the actual figure is about 1.0043 inches per second, or approximately 2.55 cm/s).

Siriometer
The siriometer is a rarely used astronomical measure equal to one million astronomical units, i.e., one million times the average distance between the Sun and Earth. This distance is equal to about 15.8 light-years, about twice the distance from Earth to the star Sirius.

Light-nanosecond
The light-nanosecond was popularized as a unit of distance by Grace Hopper as the distance which a photon could travel in one billionth of a second (roughly 30 cm or one foot): “The speed of light is one foot per nanosecond.”

Metric inch
The international inch is defined to be exactly 25.4 mm. However, this is approximated to 25 mm, to give a “metric inch”. A metric inch was used in some Soviet computers when building from American blueprints. The resulting products would seem like their American models but components were not interchangeable.

Nanoacre

A nanoacre is a unit (about 4 mm²; ≈ 2.01168 mm wide, ≈ 2.01168 mm long) of real estate on a VLSI chip. “The term gets its humor from the fact that VLSI nanoacres have costs in the same range as real acres in Silicon Valley once one figures in design and fabrication-setup costs.”

Stère
The stère (st) is equal to a cubic metre (m³), or kilolitre (kl). The stère is traditionally used to measure a quantity of wood (cf., board foot, 1 inch × 1 foot × 1 foot, or 144 cubic inches).

Sydharb
A unit of volume used in Australia for water. One sydharb is the amount of water in Sydney Harbour: approximately 500 gigalitres.

Olympic-sized swimming pool
A large Olympic swimming pool with dimensions 50m x 25m x 2m holds 2,500,000 litres, that is, 1/200,000 of a sydharb.

Shake

In nuclear engineering and astrophysics contexts, the shake (from “two shakes of a lamb’s tail”) is used as a conveniently short period of time. 1 shake = 10 nanoseconds.[8]

Nanocentury
Another derived time unit, reducing a rather large time span (century) by preceding it with a fractional prefix (nano). As Tom Duff at Bell Labs pointed out: “How many seconds are there in a year? If I tell you there are 3.156×107, you won’t even try to remember it. On the other hand, who could forget that, to within half a percent, π seconds is a nanocentury.” Computer science professor Julius Sumner Miller used to characterize the standard length of his lectures (a little less than an hour) as a microcentury (roughly 52.6 minutes, accounting for leap years).

Jiffy
In computing, the jiffy is the duration of one tick of the system timer interrupt. Typically, this time is 0.01 seconds, though in some earlier systems (such as the Commodore 8-bit machines) the jiffy was defined as 1/60 of a second, roughly equal to the vertical blanking interval on NTSC video hardware (and the frequency of AC electric power in North America).

Microfortnight
One very convenient unit deduced from the FFF system is the millionth part of the fundamental timeunit of FFF, which equals 1.2096 seconds, and is a typical example of computer nerd humour[12]. As the story goes,

“The VMS operating system has a lot of tuning parameters that you can set with the SYSGEN utility, and one of these is TIMEPROMPTWAIT, the time the system will wait for an operator to set the correct date and time at boot if it realizes that the current value is bogus. This time is specified in microfortnights.”

The joke is in having a rather large unit (fortnight) combined with a fractional SI prefix (micro) to counteract that. The practical purpose is to discourage setting such parameters without some thought. The unit was selected because the time is only approximately one second, being established by some near-infinite loops rather than a real clock unit (which isn’t active at the time), and rather than field complaints about this being “not exactly a second”, the unit was invented.

Galactic year
The most common large-scale time scale is millions of years (MY). However, for long-term measurements, this still requires rather large numbers. Using as a measure the time it takes for the solar system to revolve once around the galactic core (GY), approximately 250 MY, yields some easily memorizable numbers. In this scale, oceans appeared after 4 GY, life began at 5 GY, and multicellular organisms first appeared at 15 GY. Dinosaurs went extinct about 0.4 GY ago, and the true age of mammals began about 0.2 GY ago. The age of the Earth is estimated at about 20 GY.

Original content for publication: pub-on
Part unit of measure and part entity-in-itself, the pub-on is the quantum of material submitted to a peer-reviewed journal for publication. Manuscripts barely containing enough new information to qualify as ‘original research’ are said to consist of a single pub-on, while far-reaching works with many new and interesting results and interpretations might contain many. Publishing papers consisting of only a few pub-ons may make an author’s catalogue of papers longer, but will tend to swamp editor’s desks and confound the system for other authors. This quantity is also commonly referred to as a least publishable unit (LPU) or “publicon”

Bleeding: The Muta Scale
Used to describe how much a professional wrestler bleeds during a match, compared to a New Japan Pro Wrestling match between The Great Muta and Hiroshi Hase on December 14, 1992 in which Muta bled an unprecedented amount. The Muta is normally measured in tenths, ranging from 0.1 Muta to 1.0 Muta, 1.0 Muta is also known as a “Full Muta”. Cactus Jack is usually said to have reached 1.0 Muta in the finals of the 1995 IWA King of the Deathmatch tournament, while more recently, The Undertaker is thought to have reached 1.0 Muta in his match at the 2002 No Mercy against Brock Lesnar in the Hell in a Cell main event match, as well as Eddie Guerrero in his match with JBL at Judgement Day 2004.

Bandwidth: station wagon full of mag-tape
An observation made in the early days of Usenet that the highest bandwidth method of moving networknews across the country was “a station wagon full of mag-tape”. The phrase is attributed to many people, including Karl Kleinpaste and Andrew Tanenbaum, and has been subject to countless variations of vehicle and media types (eg “a 747 full of DVDs” or “an intern with a box full of floppies”). As a measurement unit, this is used more as a method of comparison between network technologies than as an actual hard measurement of bandwidth. It also depends crucially on the distance of the communication, e.g. “An ethernet has more bandwidth than an intern with a cartload of CDs” is certainly true over large distances – but is unlikely to be the case for short range communication. This measure also overlooks any latency involved in transferring data between the transport medium and on-line storage, which may be considerable for tape.

Laser power: Gillette
A unit described by Theodore Maiman as an early measure of laser output power. The measure was simply the number of razor blades through which the laser could burn a hole. This measurement was especially convenient as the first lasers were pulsed ruby lasers, making it otherwise difficult to measure the output power. Also, due to the relative uniformity of razor blades manufactured by The Gillette Company, it had some usefulness as a rough comparison. Thus, scientists would brag about having a “4 Gillette” laser versus their competitor’s puny “2 Gillette” laser. (For the record, Ted Maiman claims that the first laser was a “2 Gillette” laser.)

Energy: foe
A foe is a unit of energy equal to 1044 joules that was coined by physicist Gerry Brown of SUNY-Stony Brook. To measure the staggeringly immense amount of energy produced by a supernova, specialists occasionally use the “foe”, an acronym derived from the phrase [ten to the power of] fifty-one ergs, or 1051 ergs. This unit of measure is convenient because a supernova typically releases about one foe of observable energy in a very short period of time (which can be measured in seconds).

Energy: jerk
In very high energy physics, particularly in the nuclear weapons and astrophysics communities, the jerk is used as a conveniently large quantity of energy. 1 jerk = 1016 ergs = 109 joules = 1 gigajoule. This unit jerk is different from, and must not be confused with, the vector quantity jerk, which is defined as the first derivative of acceleration with respect to time.

Imagine. All these years Mrs. R. has been telling everyone how energetic I am.

## Comments

1. #1 derek
September 18, 2007

Because the parsec is a “parallax second of arc”, the astronomical unit and the parsec are intimately linked to each other via π: 1pc = 1 AU × 180 × 60 × 60 ÷ π.

But the siriometer might reasonably be called a “parallax microradian”: a star at a distance of one siriometer will trace an ellipse in the sky with a semimajor axis of exactly a microradian due to Earth’s motion around the Sun, whereas at a parsec distance it makes an ellipse one arc-second in semimajor axis. Only tradition stops astronomers measuring small angular diameters in microradians instead of arc-seconds.

2. #2 derek
September 18, 2007

I hate it when preview works and the actual comment software doesn’t.

3. #3 kevin
September 18, 2007

regarding smoots (perhaps this is just urban legend, tho): the lines are repainted by the regular city road crews, on purpose. The story goes that after a major reconstruction some years ago and new sidewalks laid down, the police dept. complained. Apparently, for years they have been using the smoot lines as reference markers for accident reports — e.g. “2 car accident 5 smoot’s west of the center point”. They had them repainted so that they could keep using their system, and not screw up all their old accident records.

-Kevin

4. #4 revere
September 18, 2007

kevin: Interesting. That must be the (former) MDC police which would not be the state police I think. I’ll ask someone in Boston to find out for me if they can.

5. #5 marquer
September 19, 2007

May we nominate new units named after prominent individuals?

Certainly the global public health community could use a few such neologisms. Perhaps those new units will eventually become recognized as SI units in their own right.

The gerberding would be a unit of failed reorganizations. Or a measure of institutional demoralization.

The chan would be a unit of conflict of interest. As a tip of the hat to its namesake, instead of referring to mega-chans, we might instead say margaret-chans.

The brownie would be a unit of flood water depth. Or perhaps a unit of delay in emergency response.

And the bush? Heh. I am soliciting suggestions on that one.

6. #6 revere
September 19, 2007

marquer: Good idea but I don’t think it has a Petreus chance in hell.

7. #7 Caledonian
September 19, 2007

My favorite unit, which I first saw used on snopes, is the measure of the incoherence of Internet message posts and/or websites: the Timecube.

8. #8 Marissa
September 19, 2007

Revere, great and facinating post. Thanks for doing the homework!

9. #9 Stephen
September 20, 2007

My school physics teacher occasionally used the light-nanosecond back in the 1970’s. I didn’t realise it ever had a wider usage.

As for the micro-fortnight, yes I recall having a good laugh when I found that one in the VMS documentation. I dimly recall later versions having a footnote along the lines of “microfortnights are now approximated by seconds”.

It’s very sad about VMS. It was the best-structured and most reliable operating system I’ve ever met. (Worked on it for three years and it never caused a single crash.) If there was any justice in the world it would be the most widely-used OS for mission-critical systems. But then the people with no technical knowledge started making all the decisions …

10. #10 JJackson
September 20, 2007

thanks for that Revere.
Now I know of the attoparsec/microfortnight I will dedicate myself to raising it to its rightful place as THE unit for speed, and will be pushing for all speed limits and car speedometers to be changed accordingly. I trust you are fully recovered from the jerks you burned preparing this post.

11. #11 tim rowledge
September 20, 2007

Just for grins, way back in my college days, we used to use micro-furlongs per millifortnight for velocity calculations. Tutors didn’t seem to mind too much 🙂

Micro-furlong is actually a reasonable length measure, being around 1/5th mm and 1/125th inch

12. #12 Stephen
September 22, 2007

My favourite is the miliHelen – the amount of beauty required to launch a single ship.

13. #13 revere
September 22, 2007

Stephen: LOL. You win.