Unit utility
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The mouseover title: "'This HAZMAT container contains radioactive material with activity of one becquerel.' 'So, like, a single banana slice?'"
explainxkcd currently fails to explain the strip's implicit reference to the entry for bogosity in the Jargon File:
1. [orig. CMU, now very common] The degree to which something is bogus. Bogosity is measured with a bogometer; in a seminar, when a speaker says something bogus, a listener might raise his hand and say “My bogometer just triggered”. More extremely, “You just pinned my bogometer” means you just said or did something so outrageously bogus that it is off the scale, pinning the bogometer needle at the highest possible reading (one might also say “You just redlined my bogometer”). The agreed-upon unit of bogosity is the microLenat.
2. The potential field generated by a bogon flux; see quantum bogodynamics. See also bogon flux, bogon filter, bogus.
The Jargon File gives this explanation of "microLenat":
The unit of bogosity. Abbreviated µL or mL in ASCII. Consensus is that this is the largest unit practical for everyday use. The microLenat, originally invented by David Jefferson, was promulgated as an attack against noted computer scientist Doug Lenat by a tenured graduate student at CMU. Doug had failed the student on an important exam because the student gave only “AI is bogus” as his answer to the questions. The slur is generally considered unmerited, but it has become a running gag nevertheless. Some of Doug's friends argue that of course a microLenat is bogus, since it is only one millionth of a Lenat. Others have suggested that the unit should be redesignated after the grad student, as the microReid.
More of the (complex and contested) background can found in the 8/29/2006 LLOG post. Wikipedia's only coverage (I think) is an entry in a List of Humorous Units of Measurement., although the dimensional analysis issues are well explained in the entry on the FFF system.
Update — My favorite unit is the scruple, which Wikipedia defines as
Stephen Goranson said,
June 25, 2025 @ 7:43 am
Reminds me of [Oliver] Smoots, the measurement units of the length of the Charles River/Mass. Ave. Bridge, starting from the Cambridge (MIT) side to Boston.
languagehat said,
June 25, 2025 @ 8:09 am
OK, I haven't felt this clueless since the physics course for physics majors I foolishly took in college (I was not a physics major), but I do not understand "the strip's implicit reference to the entry for bogosity in the Jargon File." Could someone explain?
Mark Liberman said,
June 25, 2025 @ 8:31 am
@languagehat: "I do not understand "the strip's implicit reference to the entry for bogosity in the Jargon File." Could someone explain?"
The Jargon File entry notes that the Farad (as a unit of capacitance, named after Michael Faraday) is way too large for current everyday use, wherefore the capacitors that people were/are used to using in circuit design are rated in "micro Farads", i.e. millionths of a Farad. Or even "pico Farads" ("pf"), i.e. billionths of a Farad.
The diss was then that the unit of "bogosity" should be the Lenat, named after Doug Lenat; but he was (according to the diss) so extremely bogus that everyday bogosity should be quantified in micro Lenats, namely millionths of a Lenat.
So it's a stupid nerdly joke, but I'd be surprised if this joke, and the Jargon File in general, wasn't in Randall Munroe's intellectual history, and in the back of his mind in a strip about Farads being impractically large. Of course I could be wrong.
Gregory Kusnick said,
June 25, 2025 @ 9:21 am
The power supplies in 1950s-era TVs and radios typically used large capacitors in the range of tens of millifarads. As a teenage electronics hacker I managed to collect enough of these to assemble a one-farad capacitor bank, which I used to vaporize small bits of aluminum foil.
Brett said,
June 25, 2025 @ 9:46 am
@Stephen Goranson: The name of that bridge is actually (surprisingly) the Harvard Bridge. (Amusingly, Oliver Reed Smoot later became head of the American National Standards Institute—fitting for man who was a unit himself.)
@Mark Liberman: As someone who sometimes teaches introductory E & M, I routinely have to point out to students how large a unit the farad is,* with everyday capacitances typically in the range of nanofarads (billionths) or picofarads (trillionths). And, although I was familiar with the units of bogosity, I would never have seen a connection between them and the topic of this cartoon; it seems like could be said it has about as much to do with the millihelen—the unit of beauty necessary to launch one ship.
* For those unaware, the reason the farad is so vast is that a 1 F capacitor would store 1 coulomb of charge a very modest potential of 1 volt. The volt is a reasonably sized unit; however, the coulomb is a really large amount of charge, necessitating that a 1 F capacitor be enormous. The reason, in turn, that 1 C of charge is so large is that the coulomb unit is based on a standardized magnetic force, rather than an electrical force, which turns out to mean that the coulomb ends up being proportional to c², and the speed of light c is very, very large
Not Helen said,
June 25, 2025 @ 10:11 am
@Brett — ah, the milliHelen! One of my favorites, along with the milliFermat, which is 1/1000 the time it took to prove Fermat's Last Theorem, approx 4 months. It's useful for estimating project duration.
Here's a large list of other units of measurement.
https://phrontistery.info/unit.html
david said,
June 25, 2025 @ 10:34 am
Multifarad supercapacitors have been available since the late seventies. Small ones are pretty safe to hold.
MattF said,
June 25, 2025 @ 11:09 am
@david
Correct. It is no longer necessary to tip-toe around large capacitors. We’ve discovered that a ‘large’ capacitor is basically a leaky battery.
J.W. Brewer said,
June 25, 2025 @ 11:59 am
The unit-of-measure namesake Oliver R. Smoot, Jr. is apparently some degree of cousin to Nobel physics laureate George F. Smoot III, who matriculated at MIT the same year (although presumably a few months later) as Oliver graduated. If the younger Smoot didn't manage to publish some of his Nobel-winning experimental results using smoots (or kilosmoots or what have you) as a unit of length/distance, he missed an obvious-in-hindsight angle.
Stephen Goranson said,
June 25, 2025 @ 12:57 pm
Though I was aware that that bridge was called, by some, the Harvard bridge, I recall a different bridge being closer to the link to the business school, often in news photos.
When my older brother and I drove up with a dilapidated, slow Ford station wagon and tried to merge into Storrow Drive, I narrowly escaped to tell thee.
Of course, you can't believe everything you read about Harvard.
For example, if one really wishes a diverse student body, then why seek to shut out international students?
Stephen Goranson said,
June 25, 2025 @ 1:08 pm
By the way, speaking of news photos of Harvard, I somewhat hate, loathe, and despise the NY Times' creeping tendency to avoid captioning photos with sufficient (when, where, what, who) information.
languagehat said,
June 25, 2025 @ 3:07 pm
And, although I was familiar with the units of bogosity, I would never have seen a connection between them and the topic of this cartoon
I rest my case.
David L said,
June 25, 2025 @ 3:10 pm
Tangentially related is the Kan, devised as a unit of pomposity. The base unit is so large, however, that even the most notable degree of self-regard amounts to only a milliKan.
Daniel Barkalow said,
June 25, 2025 @ 4:04 pm
@Brett
The Smoot who provided the unit of length was also the president of ISO from 2003-2004.
Viseguy said,
June 25, 2025 @ 4:33 pm
This post initially pinned my FOLI meter — Fear of Looking Ignorant — but I managed to quell my resistance by chanting "ohm". But seriously, thanks to all the helpful explanations and links, I was finally able to grok the mouseover title on my own. Fun stuff.
r-bryan said,
June 25, 2025 @ 11:29 pm
As an MIT undergrad I trudged past those smoots on the Harvard Bridge thousands of times. The numbers start at the Boston side, increasing past "halfway to hell", culminating at "364.4 smoots plus one ear". In bridge reconstruction in the 1980's, the sidewalk slabs were laid in smoot lengths, rather than the standard six feet; even the street lamps are 30 smoots apart. You could learn more than you wanted to at the Wikipedia page for "Harvard Bridge".
I once heard a lecture at MIT by Amory “Bud" Waite (you could google him too) who said, "I've been to the North Pole, and I've been to the South Pole, and as far as I am concerned, the coldest place on Earth is the Harvard Bridge in winter." He may have been pandering to his audience, but it was well received.
Jon said,
June 26, 2025 @ 12:23 am
The old unit of radioactivity was the curie, 3.7 × 10^10 disintegrations per second. Very large for many purposes. The replacement unit, the becquerel, 1 disintegration per second, is extremely small for many purposes, hence sometimes known as the buggerall. But for ambient levels of radon it is just right, so concentrations went from being referred to in picocuries per litre to becquerels per cubic metre without prefix.
The barn, a unit of area used to measure the reaction cross section of atomic nuclei is equal to 10^−24 square cm. It was called a barn because it is so ridiculously large. There was a proposal to change to a smaller unit, the shed, but it never caught on.
Philip Taylor said,
June 26, 2025 @ 3:02 am
"The unit of bogosity. Abbreviated µL or mL in ASCII" — Nonsense, surely. In this context, "mL" in ASCII would be the milliLenat, not the µL (microLenat). The ASCII for µL would be uL.
Bob Ladd said,
June 26, 2025 @ 3:42 am
@Philip Taylor: "The ASCII for µL would be uL."
Really? While mL is ambiguous, I would find uL simply uninterpretable.
I take a medication of which doses are given in micrograms. Presumably μg is the official non-ASCII abbreviation for microgram, but on the package and on my prescriptions the Greek letter is not used and the dosage is given in "mcg", or in "micrograms" spelled out.
PMB said,
June 26, 2025 @ 9:50 am
My Dad (ex radar mechanic) used to delight in charging high- voltage capacitors (about 100uF) then, just for fun and without warning, throwing them for us boys to catch… electric shocks were the norm in my childhood.
If you want a handle on nano (one billionth), 1 ns, a billionth of a second, is about the time light takes to travel from the end of your nose to the tips of your outstretched arm. And yes, u is often used in electronics and such fields as a substitute for μ. We are too busy to do the Greek.
Daniel Barkalow said,
June 26, 2025 @ 1:02 pm
@Bob Ladd
In engineering fields, "u" is used as the character on a US keyboard that is arbitrarily assigned as the prefix meaning "micro" in abbreviations. It's too easy to make a mistake typing "mcg" and get a result that's valid but dangerously wrong, and using a letter as the abbreviation that's not in the thing being abbreviated isn't actually more difficult once people get used to it. As an example, if you put "c * 5us" into Google, its calculator will identify that unit as "microseconds", whereas "c * 5mcs" requires AI to figure out what you seem to be asking.
Andreas Johansson said,
June 26, 2025 @ 1:56 pm
I deal with micro- units fairly regularly, and I dunno if I've ever seen the "mc" abbreviation.
(Mu is easily available on my keyboard – AltGr+m – but when I'm typing on the phone or similar, as now, I use 'u'.)
J.W. Brewer said,
June 26, 2025 @ 4:35 pm
Note FWIW the use of "pound" in the second frame that deviates without explanation from the metric units in the other three, presumably because "gram" is also badly-designed scalewise (at least if a rock is the prototypical thing you want to talk about the weight of*) and using "kilogram" would have given the game away – i.e. reminded the reader there are in fact multiple contexts within the metric system where one does not, in fact, use the theoretical "base" unit as the normal conversational base unit.
*I didn't have great intuition about the weight of pebbles (which could have been used instead in that second frame) but when I asked google its "AI Overview" feature said a pebble typically weights between 5 and 20 grams, which sounds plausible.
J.W. Brewer said,
June 26, 2025 @ 4:49 pm
Using e.g. uL for µL is workable in, but only in, a context where the range of glyphs that could plausibly appear as prefixes to L is limited and well-known. Otherwise, you run into the problem that e.g. ASCII u looks even more similar to υ (lower-case Upsilon) than it does to µ, so the substitution only works because lower-case-upsilon-liter is not understood to be an available unit of volume. Better to stick to scruples, as myl noted in the addendum to the OP.
Jon said,
June 27, 2025 @ 1:11 am
The use of the Greek letter µ is a serious problem for the SI system. Some printing systems recognise it as a Greek m, and not having that glyph, substitute a Roman m.
Results of measurements are thus reported as a thousand times bigger than they should be.
This happened in the wake of the Fukushima accident, when radiation doses of microseiverts were printed in academic journals as mSv instead of µSv. Some journals now suggest writing the word out in full to avoid the problem.
Using mc instead of µ is an ugly bodge, but in my opinion it is the best solution.
Philip Taylor said,
June 27, 2025 @ 2:04 am
Never having previously encountered "mcg" as an ASCII representation of "microgramme", I would without other guidance have interpreted it as "millicentigramme", or ten times its intended mass.
Renegade Geek said,
June 27, 2025 @ 5:17 am
"The slur [of naming the unit of bogosity after Doug Lenat] is generally considered unmerited"
Was the slur in fact unmerited? In my experience many years ago, working with the late Douglas Lenat, the slur was entirely merited, earned every day by the man's words and actions.
For more on Lenat's career, see Yuxi Liu's recent retrospective. A long read, but interesting and detailed. https://yuxi-liu-wired.github.io/essays/posts/cyc/
Philip Taylor said,
June 27, 2025 @ 6:03 am
"After 40 years, […], Cyc has failed to reach intellectual maturity, and may never will."
"may never will" ? That doesn't feel right to me. Either "perhaps never will" or "may never do so" would seem better to my mind.
Andrew Usher said,
June 27, 2025 @ 7:35 am
Re 'mc' for 'micro':
This seems to be used only in US medicine, where it was established specifically to prevent confusion for 'milligram' with 'microgram', and for that reason deserves to survive, even if it's non-standard. Apparently in other countries people are told to write 'microgram' in full to distinguish, but that seems it might actually be less clear.
In all other contexts, as far as I know, 'u' is the only alternative to the Greek letter. It does have the merit of being unambiguous, at least when it preceding the unit grams; it could mean nothing else. As Philip Taylor points out, it is easy to read 'mcg' is 'millicentigram' (a tenfold error) if not familiar with the convention, but I'm sure all Americans in the medical industry are.
"May never will" is just a blunder.
k_over_hbarc at yahoo.com
Andrew Usher said,
June 27, 2025 @ 7:46 am
Also, as far as I see, the Jargon File doesn't even mention farads in this connection. Perhaps saying that a milli- or micro- whatever is the largest practical unit could be an oblique reference, but as others have pointed out, there actually are real capacitances measured in farads, and the unit is not so pointless. Also, Americans likely won't think of volts and farads as metric units, just _electrical_ units – which is how they were originally intended, before being co-opted by the SI juggernaut.
Bob Ladd said,
June 27, 2025 @ 9:53 am
@Andrew Usher:
Not just US medicine, perhaps general anglophone? I live in the UK, and the medications I mentioned in my original comment are prescribed and dispensed by the NHS. I suppose it's possible they are manufactured in the US, but I doubt it.
Russinoff said,
June 27, 2025 @ 10:35 am
"In my experience many years ago, working with the late Douglas Lenat, the slur was entirely merited, earned every day by the man's words and actions."
Having occupied an office down the hall from the two of them those many years ago, while I agree with Renegade Geek's assessment, I am convinced that Lenat's reputation has suffered less from questionable research practices than from a profooundly unlikable personality.
Gav said,
June 27, 2025 @ 1:35 pm
Regarding farads, a friend of mine who is still with us, just about, did his national service with the RAF in the early 1950's. He tells us that one day, in the spirit of fun, they gave him a stick and told him to climb into this bomber and to discharge the capacitors on the aircraft's RADAR. He poked at the thing with the stick provided and was thrown several feet across the fuselage. On another occasion, stationed in Germany, they gave him another stick (well, a pickaxe handle actually) and told him to stand guard over some of the UK's fleet of front line V-bombers that were parked on the apron. He did actually enjoy his brief stint in the RAF.
Matt McIrvin said,
June 29, 2025 @ 5:31 am
I went to high school and took AP Physics along with Oliver Smoot's son Steve. He subsequently went to MIT and I heard they re-measured the bridge in units of Steve at some point–he was very similar to his father in height
Matt McIrvin said,
June 29, 2025 @ 7:49 am
"Also, Americans likely won't think of volts and farads as metric units, just _electrical_ units – which is how they were originally intended, before being co-opted by the SI juggernaut."
The electric units *are* fundamentally metric, though, related to each other through SI length, time and force units. The coulomb is derived back from the ampere, which was originally defined in terms of magnetic force between wires at a standard distance of 1 meter, with the constant of proportionality defined as a nice round number in newtons (though lately it's been redefined by fixing the charge on the electron, since that is more precise today).
It's just that electricity became a thing to talk about in detail late enough that the first attempts to define units for it were made by scientists with access to the metric system, so there was never a chance for a different set of "traditional" units to take hold.
However, there was a profusion of different systems of electrical units that came from different choices of *how* to use metric–whether you used cgs or mks metric units, and where you put the factors of 4pi in the formulae. Old editions of Jackson went on about this at some length–don't know if they still do.
Matt McIrvin said,
June 29, 2025 @ 8:00 am
(The farad is big because the coulomb is big, and the coulomb is big because it's an ampere-second and the ampere is a pretty hefty chunk of current–not unheard of in practical applications, but big, definitely enough to kill you good. Milliamps and microamps are often encountered in technical applications.)
Andrew Usher said,
June 29, 2025 @ 8:44 am
You aren't wrong, but that's perhaps misleading. First, the two different kinds of systems you mentioned ought to be distinguished.
The standard electrical units we all know, including the volt, farad, ohm, etc., are what was originally called the 'practical' electrical units, meaning they were intended for 'practical' applications of electricity and not necessarily science. Yes, they were defined ultimately based on metric units, but that wasn't of great importance at the time compared to having a standard with (mostly) practical-sized units. In fact it seems that no one cared that the watt and joule were exactly the coherent MKS units of those quantities (they could as well have been different by a power of 10), as all scientists then that cared about coherence used cgs.
On the other hand, your last paragraph references the systems of EM units used by scientists, for both theory and (partly at least) experiment. There were indeed several possible standards there, but (excepting natural units) the alternatives were based on cgs, as that is what scientists were used to at the time, and there was no compelling reason to change. In practice change would mean accepting the SI 'practical' units, which are physically wrong for the theory of electromagnetism. In theory, the exact magnitude of the units is almost not important compared to how they relate to each other; and it is there that SI units fail.
Jon said,
July 2, 2025 @ 4:03 pm
Note at the end of an article yesterday on the Guardian website:
This article was amended on 1 July 2025. An earlier version used the Greek letter mu as part of the abbreviation for micrograms, but a technical issue means this character cannot be rendered on some devices. The abbreviation mcg has been used instead.
https://www.theguardian.com/environment/2025/jul/01/pfas-forever-chemicals-water-contamination-saint-louis-france-aoe
ajay said,
July 3, 2025 @ 9:35 am
the ampere is a pretty hefty chunk of current–not unheard of in practical applications, but big, definitely enough to kill you good
It's certainly, by far, the unit that most people are likely to encounter in their everyday lives, because it's the unit that household current is measured in – particularly when it comes to things like fuses and circuit breakers.
maidhc said,
July 5, 2025 @ 2:32 am
Thank goodness that the electrical world never developed American and Imperial units, or instead of V=IR we would have V=133.4 x10**5 IR in whatever horrendous units had turned up.
There is, however, the BTU — "the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit."
And thankfully the Imperial system has the same pound as the American, even if gallons are different.
TonyK said,
July 5, 2025 @ 9:26 am
PMB, light travels less than 30cm in one nanosecond. You must have very short arms!
Philip Taylor said,
July 6, 2025 @ 4:05 am
There is, however, the BTU — "the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit" — only for the younger generation, Sir. For those of us old enough to remember, the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit is the BThU ("British Thermal Unit"), not the BTU ("Board of Trade Unit").