Cursed Units

A collection of cursed scientific units.

Some small corrections: the distances between the planets in the graphics should be between their centres, and the wording when describing the pulse delays is backwards at one point. Some commenters explained that the 2 astronomical units is because the distance between the measurements is twice the distance from the earth to the sun. I know that; I’m jokingly questioning why the definition of the parsec doesn’t have the factor of 2 included (I also know why it doesn't, this joke wasn't communicated very well).

If you know any other cursed units, share them in the comments! Some of these are in Cursed Units part 2, but here's some more...

Noise in a voltage signal is measured in V/√Hz (volts per square root hertz).

You would expect the amount of data produced by a particle collider over a time period to be measured in bytes or number of collisions, but apparently it's measured in fb^-1, inverse femtobarns, a barn being roughly the cross-sectional area of a uranium nucleus.

Multiplication and division of units is all well and good, but it breaks down when you're working with units on logarithmic scales, like pH, decibels, or stellar magnitude.

Sheet resistance, the electrical resistivity of rectangular sheets of materials, is measured in Ohms per square. Not square metres, not square inches, just square. This is because resistance across a rectangle is proportional to length and inversely proportional to width, so it depends on the aspect ratio but not the size.

Other bizarre combinations of units mentioned by commenters: thermal effusivity is measured in J/(m^2 K s^(1/2)), a Jansky in radio astronomy is 10^(-26) W/(m^2 Hz), and electrical capacitance is measured in Farads which are kg^(-1) m^(-2) s^4 A^2.

A lot of commenters suggested various imperial units. To me these aren’t cursed in a particularly deep way, since they just involve a conversion factor. I’ll give a special shout-out to acre-feet though.

[robertyang]

I love how it feels like the background music is equally upset about all of this as the narrator

[strawmann]

"I personally find square roots cursed" ~Pythagorean Cultist, most likely

[AntonioZL]

The hubble constant being simplified to Hertz and then it's inverse ending up as an approximation of the age of the universe absolutely blew my mind.

[jaywu]

In middle school I wondered why rain was measured in mm instead of something logical like litres/m^2 until it clicked and I realized they are the basically the same unit.

[parkerkincaid]

Calculating the Hubble constant as a music note (all notes are just frequencies) gets us an E 67 octaves below middle C.

[ptorq]

In my PChem class the instructor made the error of saying he didn't care what energy units we used on a test. He really meant it didn't matter to him whether we used joules or calories, but I took him at his word and turned in my test with all the energies expressed in liter-atmospheres.

[NevinBR]

The sun appears to move through the sky at a rate of 15 minutes per minute.

[JohnDixon]

I once had a physics problem recommend writing the charge of an electron as "1 electronvolt per volt" in order to help the units cancel nicely. I'll never forget staring at that problem and just thinking, "Huh, well I guess that's technically true"...

Now that I'm an astronomy grad student, I see shit like "solar masses per year" and "joules per square centimeter per second per Hz" and it doesn't even seem out of place.

[noscar]

3:33 "using kWh is like using km.h^-1.min" that's basically what we do by measuring distance using light years

[Tandanuu]

Another great unit for power can be found on energy efficiency labels for light bulbs here in the EU. It's specified in kWh/1000h :D

[joostvisser]

I needed to pause for a second when you revealed that the Hubble constant can be measured in Hz. That is truly cursed

[evinism]

The little detail of the piano seemingly following a random walk on a whole tone scale while random walks are being discussed is amazing

[cvl]

I've seen in the notes of a friend of mine attending a urbanism class the unit "people/dumpster", which was used to measure how many people would be served by a single dumpster in a particular area. The first time I saw it I found it very funny, I read 500 people/dumpster as 500 people crammed into a single dumpster

[TheLoneWolfling]

My favorite is s^-1 / s^-1, where the units don't actually cancel.

(One is a frequency, the other is an _angular_ frequency, and so is off by a factor of 2pi.)

In general, anything involving radians is 'fun', because people declare it to be unitless and then omit the unit, and then get really confused.

[skurella]

The craziest unit I’ve ever worked with is an Erlang, which is equal to 60 minutes per hour. You read that right. It’s used by telecommunications engineers to describe the capacity of trunk phone lines (i.e. between exchanges) to carry multiple voice calls simultaneously. If you group 10 regular phone cables together, it will have a capacity of 10 Erlangs. Long live engineering.

[michaelwoodhams]

Back when I was an astronomy grad student (c1990) one of my professors told us "a barn megaparsec is a teaspoon". I quickly responded "That can't be right - maybe 0.6 teaspoons?"

The reasoning being: I knew a parsec was 3 x 10^something meters, a teaspoon was 5 ml = 5 x 10^something m^3, and a barn was 10^something m^2. So taking on trust that the powers of 10 cancelled as he claimed, there was still a factor of 3/5 left over.

A bit later, I showed him on my shiny new HP48SX calculator, which could attach units to quantities and do conversions, that multiplying a megaparsec by a barn and converting the result into teaspoons indeed gave a result of about 0.6.

That HP48SX's units functionality was absolutely wonderful for an astronomy grad student.

[beriukay]

The musical companionship to the monologue is frickin' amazing. I noticed it early on, but at the random walk, I decided I had to comment on it

[FireworkerK]

There's an XKCD comic with a cursed measurement resulting from unit conversion. The unit is meters and Randall Munroe called it the "Oily House Index (OHI)".

He noticed that real estate prices are stated in dollars per area while oil prices are dollars per volume.
By cancelling these two units against each other, you get the OHI measured in meters. He then graphed it over time and some economical events even showed up (housing crisis, oil crisis, etc).

The "intuitive" representation of the OHI would be: if I sold a piece of real estate and bought crude oil from that exact amount of money, how high could I fill the property with the oil I bought?

Its absolutely lovely and the corresponding comic is one of my absolute favorites.

[Space_Kalak]

The most cursed unit I came across in my physics degree was for the frequency spindown rate of a pulsar, measured in seconds per second (or, every second, how many seconds longer each rotation of the pulsar increases by)

[ReySilverskin]

One thing that I always chuckle at is that torque can theoretically be measured in joules.