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Uno – the “unit” for dimensionless quantities
- anthk 5y agoIt classes with Spanish on naming quantities, it feels wrong. Name it "unitas", far better.
- Synaesthesia 5y agoInteresting idea. We generally just say "unit" if necessary. >In 2004, a report to the International Committee for Weights and Measures (CIPM) stated that response to the proposal of the uno "had been almost entirely negative", and the principal proponent "recommended dropping the idea".[15] To date, the uno has not been adopted by any standards organization, and it appears unlikely that it will ever become an officially sanctioned way to express low-value (high-ratio) dimensionless quantities. The proposal was instructive, however, as to the perceived shortcomings of the current options for denoting dimensionless quantities.
- gerdesj 5y agoQuite. Unit is quite literally the same as Uno if you squint a bit. Both are Latin derived and both mean "one" - more or less. However I will accept that unit is overloaded somewhat and I don't know much about the way that Spaniards use uno in their spare time. So using a word that means one and then fiddling around with prefixes is either really clever or really daft depending on which side of the bottle of wine you happen to be. On balance, for me, I'd be grateful if you leave one alone. To me it means a Platonic One which is unobtainium but I'll let you have one anyway! But only the one (no not that one, the other one.)
- riffraff 5y agoI'm Italian, where uno also means uno, so I'll offer my perspective. As a kid I was taught to use "unità" (unit) to refer to the numbers below ten (e.g. "add up the units first, then carry the tens.."). It is also used as an "accounting" unit (e.g. "there are 3 units left") in some cases, tho probably less commonly than in English, as it's often implicit. So yeah, unit seems a clear better choice than abusing the number one.
- ConceptJunkie 5y ago> As a kid I was taught to use "unità" (unit) to refer to the numbers below ten (e.g. "add up the units first, then carry the tens.."). Arithmetic instruction in English uses "unit" in the same way. However, since "unit" is a highly overloaded term, I think the idea of "uno" is a good one, at least for English. For Italian and Spanish, etc., probably not so much.
- scrooched_moose 5y agoThe biggest conflict I see is in many fields were you are dealing with dimensionless numbers, you are dealing with a lot of them once. Having to specify "With a Reynolds number of 1300 U and a Prandtl number of 1 mU" is a lot more cumbersome than common convention of "With Re=1300 and Pr=1e-3".
- dhosek 5y agoThere's also the problem that 1U×3U=3U² and the fact that you wouldn't be able to add 3U² to 2U since the'd be different units.
- tomrod 5y agoAye, but 1^2 is 1,so it's a bit of a special wash. Like 0!.
- dhosek 5y agoThe problem is that U isn't 1, it's meant to be a unit, but then it doesn't behave like a unit in which case, why bother with it at all?
- BlackFly 5y agoThis isn't a problem in practice though, you just get "strange" constants with units equal to some negative power of U in your equations. The same thing happens when you move from electrostatic units to SI: suddenly Coulomb's constant appears. Many people advocate ESU for precisely that reason: no Coulomb's constant.
- deleted 5y ago[deleted]
- exporectomy 5y agohow is 1 mU more cumbersome than 1e-3? The whole point of the prefixes is to avoid those cumbersome exponents, isn't it?
- ConceptJunkie 5y ago
- SilasX 5y agoIn structural engineering, strain is a unitless quantity (length expansion per unit length) and in my aerospace job we would express parts per million of strain as microstrain. (I expressed my pitiful raise as 20000 microstrain.)
- navane 5y agoSometimes we keep the units though, and express strain in mm/mm. "The strain limit for S355 is about 0.02 mm/mm." A mathematician might eliminate them against each other, for a phycisist it's a reminder of what its definition.
- SilasX 5y agoGood point. I also really shouldn’t say strain is unitless, just a case where the units happen to divide out.
- lalaithion 5y agoThe number 1 isn't the SI unit for dimensionless constants. The SI unit for dimensionless constants is 602214076000000000000000. No, "amount of something" or "number of atoms" is not a different unit than dimensionless constants; that would be like if the SI unit had "the amount of charge held by 10^30 electrons" as a different unit than "charge".
- minitoar 5y agoI don’t get this. What do moles have to do with dimensionless values?
- deleted 5y ago[deleted]
- prutschman 5y agoI think they're referring to the fact that there is one dimensionless base unit already standardized in SI: the mole. There aren't two length units, so there "shouldn't be" two dimensionless ones. (Whether they were trying to be funny or not I couldn't tell you.)
- gerdesj 5y agoIt's a mol not a mole (sounds the same) lol (or is that lole?) "they" are not trying to amuse anyone.
- drdeca 5y agoHow do you know that lalaithion was not trying to amuse anyone?
- prutschman 5y agoThe "mole" is the unit, "mol" is the symbol for the unit, like with "kilogram" and "kg".
- dragonwriter 5y ago
- crazygringo 5y ago> In 2004, a report to the International Committee for Weights and Measures (CIPM) stated that response to the proposal of the uno "had been almost entirely negative", and the principal proponent "recommended dropping the idea".[15] To date, the uno has not been adopted by any standards organization, and it appears unlikely that it will ever become an officially sanctioned way to express low-value (high-ratio) dimensionless quantities. That sounds... about right, ha!
- ggm 5y agoI'd have voted for burflydick or mumbledypeg or doohickey A better reasoning for why SI needed a formalism of a unit for dimensionless value would possibly have helped. Almost universal negative dislike speaks to a committee on a mission without a good sense of "do we need a reality check here" c/f "brontosaur" and "pluto"
- dragonwriter 5y ago> I'd have voted for burflydick or mumbledypeg or doohickey Or “radian”. Oh, wait...
- ggm 5y ago"decibels"
- SV_BubbleTime 5y agoNothing wrong with radian… except that I keep having to explain to people it’s not metric. “It’s one Honda Civic across, at 1000 Honda Civics away”
- 6gvONxR4sf7o 5y agoI've often felt it to be helpful to treat dimensionless quantities as a smell that the dimensions might be too unspecific. 12 meters / 3 meters is just a unitless 4, but 12 meters east / 3 meters north is a much more interesting 4 units-east-per-unit-north. Keeping track of these invariant "hidden units" was sometimes helpful to me in physics classes, especially in later classes where nondimensionalizing your equations was so handy.
- TeMPOraL 5y agoOn a related note, I've been dealing with some process chemistry recently, and I've noticed that a lot of dimensionless quantities that are ratios retain their original units - I've seen many cases of units like e.g. [kg/kg]. Not sure what's the reasoning behind this, but I suppose this prevents mixing up [kg/kg] with [m/m] and other unrelated ratios.
- jimmaswell 5y agoIf it's something like milligrams of X per gram of Y I think it's generally better to just write it like (mg X)/(g Y)
- gerdesj 5y agoIf you are having snags with dimensionless ratios in chemistry, why not talk to any half competent cook/chef? They don't piss about like that! The reason your quantities (LMT etc) are dimensionless is because you need to bake a decent cake or mix a cocktail and get a grip 8) I am being flippant but I don't think that mixing kilos and meters in any unlikely ratio is likely to end well. They tend to become quite forceful if not mixed carefully.
- FabHK 5y agoIn my experience, people have quite some trouble with basis points ("The fund charges just 5 bp per year", which means 0.05% per year), but I doubt that "The fund charges 0.5 mU (or 500 µU) per year" will help much. It does have a certain elegance, though.
- talaketu 5y ago"The fund charges 5bp" doesn't make sense to me! I understand basis points to be absolute difference in some rate, where the rate was expressed as a percentage. So, if the interest rate was raised from 5% to 5.25%, we don't say the increase was 0.25% (because that could be interpreted as understating the change) and we don't say the increase was 20% (0.25% / 5%) because likewise that would overstate the change. We say the increase was 25 basis points to avoid any confusion.
- lupire 5y agobp is a percentage of a magnitude, whether a difference or not. It's value is that it is not a percentage of a percentage or a rate.
- lucb1e 5y agoI needed this in the past but didn't know of it! It seems convenient, because when you write km and kWh in some places and then just write 'k' behind another number that is simply a unit, it looks like you're missing something, or might have written Kelvin in lowercase, but really you mean a thousand units. Writing kU is then unambiguous. Not sure why `response to the proposal of the uno "had been almost entirely negative"` according to Wikipedia. Does anyone know more about that? It's not as if I need this daily, most times it's clear from context, but still I remember wishing for such a unit in the past.
- dragonwriter 5y ago> Not sure why `response to the proposal of the uno "had been almost entirely negative"` according to Wikipedia. SI already has at least two different unit names for dimensionless 1 (rad and sr), so a third identical unit was probably seen as superfluous.
- HPsquared 5y agoRadian and steradian are specific to measurement of angles. You wouldn't provide a Reynolds number in radians, for example.
- reikonomusha 5y agoAs someone who works in science, it’s because it mostly feels like a solution looking for a problem. The “unit” U gives the same vibes to scientists as some classes/abstractions thought up by creative programmers feel to software engineers. Imagine your colleague saying you should use a function called def doc(val, docstring): if __debug__: print("using value described as %s" % docstring) return val like in x = doc(5, "number of fingers on one hand") because “this leads to incredibly readable code, and the compiler won’t compile it if you don’t include the string.” Could it be valuable in principle? Sure. In practice? Just a nuisance. A comment will do. I don’t think I, or my colleagues, have ever run into an issue with ambiguity arising from unitless quantities.
- 5y ago
- dkackman11 5y agoThere is also the internationally recognized and ISO standardized, unit of the Yahtzee (symbol Y!), which is any five digit number between 11,111 and 66,666 (inclusive) comprised of the same digits.
- dane-pgp 5y agoThere were some objections to that unit being standardized, but the precedent had already been set when they approved the Dominoes unit (symbol D), which is used for two digit numbers between 00 and 66 (inclusive).
- aendruk 5y agoThat looks familiar. https://news.ycombinator.com/item?id=27597433 https://news.ycombinator.com/item?id=27597433
- remram 5y agoAn alternative is to use the prefix only, e.g. 500m (=0.5), 700n (=0.0000007), 5.1k (=5,100). This is easy enough though it can clash with non-standard multiples (MM suffix, M misspelled as m, B for billion, ...). The U is quite unnecessary.
- jonsen 5y agoYour first example is a clash, 500 meter.
- remram 5y agoI suppose you need some context. When I read "cpu": "500m" in Kubernetes, I know it's half a CPU, but you are right it's ambiguous stand-alone. Hmm.
- jonsen 5y agoWe have 500‰ for 500 unitless milli. And there are more: https://en.m.wikipedia.org/wiki/Parts-per_notation https://en.m.wikipedia.org/wiki/Parts-per_notation
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- IncRnd 5y agoI and everyone I know has used either "utils," "units," or "U" for such units. Uno is a direct reference to the UN, specifically United Nations Organization. Or maybe it is one in Spanish. Please stop trying to create new things that aren't needed and end up trampling on the rest of the language.
- peterfield 5y agohttps://en.wikipedia.org/wiki/List_of_unusual_units_of_measurement https://en.wikipedia.org/wiki/List_of_unusual_units_of_measu... is one of the most entertaining wikipedia page :) I love the SydHArb
- oasisbob 5y agoIf you like that, make sure you check out the `definitions.units` file from GNU Units. Many informative and entertaining rants to be found there: https://fossies.org/linux/units/definitions.units https://fossies.org/linux/units/definitions.units
- Rayhem 5y agoI had a hand in fixing this to properly handle Gaussian EM units! It took a bit of doing to make grams^0.5 viable...
- yesenadam 5y agoAm in Sydney, never heard of the supposed Sydharb before now. Olympic swimming pools is very common though. As are the more informal crap-ton and shit-load.
- alanbernstein 5y agoOne of the entries is the rack unit, 1.75 inches, or 1U, amusingly.
- KirillPanov 5y agoIt's sad this didn't catch on. It's particularly handy when you move to "square unos" (like "square millimeters" but dimensionless). For example, in microchips the sheet resistance of layers (metal, poly, etc) has units of "ohms per square uno". This is because a 1mm*10mm sheet and a 10mm*100mm sheet both have the same resistance (along the first axis). The latter sheet is longer (higher resistance) but wider (lower resistance) and the effects cancel out. So it's really "ohms per width-to-length-ratio", but width-to-length-ratio is a unitless quantity (mm per mm = mm/mm = uno). Everybody call this "ohms per square". Frankly that just sounds weird, and grammatically invalid. Ohms per square what? Parse error. Before I heard about unos I would occasionally call it "ohms per aspect ratio" but I'm probably the only person who uses that terminology. https://en.wikipedia.org/wiki/Sheet_resistance#Units https://en.wikipedia.org/wiki/Sheet_resistance#Units
- jonsen 5y agoI think ‘ohms per square’ is fine. Just like e.g. ‘seconds per radian’ is much better than ‘seconds per uno’. Uno is generic and tells nothing about the context.
- KirillPanov 5y agoIn this case it would be "ohms per square uno", not "ohms per uno". It's got all the same context as "ohms per square". In fact it has all the same words! Also radians are not unitless; they are fractional cycles, not ratios.
- jonsen 5y agoAs another commenter said, a square is a unit of the plane; a square figure; all sides equal. Likewise a radian is a unit of the plane; a pie-slice figure with all sides equal.
- KirillPanov 5y agoPie-wedge-shaped things are not the only use for radians. The phase [1] across a Josephson Junction is measured in radians, but there are no planes involved. The progress of a longitudinal wave [2] as seen passing a stationary observer is measured in radians per second, yet no plane is involved -- it works just fine in a one-dimensional universe. Radians measure cycles. If you limit yourself to geometry then sure, radians seem like a thing for measuring circles. But that's just a side effect of the fact that the only cyclic symmetries of Euclidean space are rotations. So the only cycles you're going to find in high school geometry will be related to circles. [1] https://en.wikipedia.org/wiki/Josephson_phase#The_Josephson_equations https://en.wikipedia.org/wiki/Josephson_phase#The_Josephson_... [2] https://en.wikipedia.org/wiki/Longitudinal_wave https://en.wikipedia.org/wiki/Longitudinal_wave
- CyberRabbi 5y agoThis breaks type checking expressions of many different units. For instance, 1 meter times 1 meter is 1 meter squared. 1 uno times 1 uno will come out to 1 uno squared but the answer should be 1 uno. Is there a systematic way to deal with this?
- jonsen 5y agoIf unit calculations can reduce e.g. m^3/m -> m^2, why shouldn’t it reduce U^2 -> U ?
- CyberRabbi 5y agoYou can simplify but it’s still unclear if the U^2 term you derived was supposed to be U^1 (before the simplification, I.e. you did an extra multiplication). It just makes bare type checking slightly more ambiguous.
- foxes 5y agoWhy does no one ever formalise units - what are units? A ring group R[G] over some symbols {L,T,..}? It would it would make sense to have an identity. The fact when we do physics its over R^n[G] or C^n[G] never really seems to be important though.
- feoren 5y agoYou might be interested in https://terrytao.wordpress.com/2012/12/29/a-mathematical-formalisation-of-dimensional-analysis/ https://terrytao.wordpress.com/2012/12/29/a-mathematical-for...
- foxes 5y agoYeah I mean it could help for essentially type checking your work. I feel it’s common in physics to set a lot of units to “1” which is just like a morphism to the underlying field, and then later you put units back in. Obviously you can do calculus/algebraic geometry etc over more interesting objects than just a field, that seems to be the essence Tao post. I am not entirely sold on torsor perhaps.
- anonytrary 5y agoMy physics professors always just said "unit" or "unity". Never heard of "uno" before now.
- thedudeabides5 5y agoDon’t we already have a word for this? One
- jonsen 5y agoThe I in ISO stands for international mein lieber freund.
- beardyw 5y agoI have often hit up against zero requiring units. A distance of zero is just zero. Apply units to it if you want but it is just as happy without. CSS to its credit allows zero without px or em etc. Most software misses this point. I have had to set up details of a person with little more than their name, then being required to provide a currency for their zero value account. It's like saying a field is empty and being asked what animals it is empty of.
- nlitened 5y agoIt does not work for all units though: e.g. temperature units (degrees Celsius, Fahrenheit, Kelvin)
- geoalchimista 5y agoI've never seen this "uno" unit appearing in any scientific paper. Makes me wonder what the intended audience is, besides the committee that proposed it.