Looks like I never learned this though I write a lot of numbers with metric units.
1cm?
1 cm?
1-cm?
1g
1 g
1-g
I vacillate between the space or no-space versions. Is one way, the ‘correct’ way?
The “correct” way regarding spaces or not varies by location and available space. There are countries/languages which tend to write it with the space and others without. The version with the dash: please no, those are scientific terms, not accounting entries (insert here as many exclamation marks as desired).
I have never seen the hyphen used by anyone.
I personally was taught to leave no space between the number and the unit, but section 7.2 of this suggests a space as an editorial convention. I imagine neither space nor no-space is considered “more correct” except by a given editorial staff (although, again, either is better than the hyphen).
It is a unit and most (at least every one I have encountered) scientific journals use a space between number and unit and a space between multiple units (1 g, 1 mL, 1 M^-1 s^-1, 32 kg m^2).
The way to remember is that 1 m is just a counting system using a unit similar to using 1 cow, 1 block, and 1 good question.
This, I like
I’m in the space camp. (Cool, I’ve always wanted to to Space Camp.) As I do with many grammar problems, I imagine what it would look like written long. For example, would you write 48kilograms or 48 kilograms? The abbreviated form really doesn’t change anything. Plus, you run into the problem that, in some fonts, the numeral ‘1’ is indistinguishable from the letter ‘l’ so there’s that.
There are interesting exceptions, however. According to the NIST style guide…
A space is used between the number and the symbol to which it refers. For example: 7 m, 31.4 kg, 37 °C.
*When a metric value is used as a one-thought modifier before a noun, hyphenating the quantity is not necessary. However, if a hyphen is used, write out the name of the metric quantity with the hyphen between the numeral and the quantity. For example:
a 2-liter bottle, NOT a 2-L bottle;
a 100-meter relay, NOT a 100-m relay;
35-millimeter film, NOT 35-mm film
Spaces are not used between prefixes and unit names nor between prefix symbols and unit symbols. Examples: milligram, mg; kilometer, km.
I agree. I would use the space. Also, and maybe I’m in the minority here, but seeing something like “2m” makes me think of “2 multiplied by m” rather than “2 meters” in the way that “.9c” means “.9 of the speed of light in a vacuum.” Obviously, context will offer up the right interpretation, but, still, I prefer the space partly for that reason, too.
The standard convention for metric units is that their symbols are capitalized if they are named after someone (e.g. “J” for Joule, “P” for Pascal) but not if they are just words (e.g. “m” for metre, “g” for gram). The one exception to this rule is the litre, which has capitalized symbol “L”, for precisely that reason – to avoid ambiguity with the numeral “1”.
Of course someone then invented the biography of the little-known physicist “Agustin Litre” (and his daughter, Mille) who did groundbreaking research into volume measurement and got the unit named after him in his honour.
Good point. I always wondered about that. Still, there’s the lumen (lm) and lux (lx) which would look weird without the space.
But note the names of the units do not get capitalized. The “Joule” above for example would be the person, as in “J” is named for Joule, and to spell it out, the joule is named after him.
And while we’re at it, the base unit of temperature is the kelvin, not the “degree Kelvin”. Water freezes at about 273.15 K, not 273.15°K or what have you. Furthermore, and related, the abbreviation for “kilo-” is not capitalized. 1000 g = 1 kg, not 1 Kg.
And don’t even get me started on computing abbreviations. Kilo- means 1000, not 1024. (There’s a whole set of powers-of-two prefixes. Use them!) The abbreviations for byte (B) and bit (b) are different only in capitalization, and hence that capitalization matters. A pox upon everyone who writes “1 Kb” to mean “1024 bytes”!
Fun fact on this: Everyone remember the final incarnation of floppy disks? The 3.5" ones? Well, their final capacity ended up being marketed as “1.44 MB”. This was neither 1.44 million bytes, nor was it 1.44 MiB. It was, actually and bizarrely, 1440 KiB, or 1.406 MiB, or 1.474 million bytes (note that Microsoft uses SI prefixes incorrectly as binary prefixes, as does the majority of consumer-facing software and hardware documentation).
Just to add, when writing out a number < 1 in a decimal, always have a leading zero… However, when writing a number > 1, never have a trailing zero.
i.e. 0.5 mg is acceptable, .5 mg is not… While 473 mL is ok, but 473.0 mL is not.
It’s quite appropriate to have a trailing zero, provided it is significant. In other words, its presence implies a certain level of precision: “I have measured the volume of this liquid to be, not 472.9 mL, not 473.1 mL, but 473.0 mL. It may indeed be 472.97 mL, or 473.01853976 mL, but my instruments have verified the value in the first decimal place.”
When I was in high school, we were taught to write the L for liter in lower case cursive to avoid confusion with a one. Any time I saw it in college, it was lower case. When I retired from teaching science in 2010, the capital L had been used for a while, but I still had lots of glassware with ml (some with a script l) and some with mL.
I’d still like to know why Georgia public schools seem to have abandoned the words alkali and alkaline in favor of the less precise base and basic. Do other states prefer base to alkali?
In my experience, 473 means something different from 473.0. One number had more precision.
ETA: too slow.
True… depending on where you are writing this info… In my own experience, it depends on where the information is written. In my line of work, I see and write SI units all the time… But, I work in the medical field (Pharmacy), where we are worried about major errors. If someone doesn’t do a leading zero, then the decimal can be easily missed leading to a ten-fold error… Same with a trailing zero, if you have one, we might give a ten fold error dose…
So basically… Significant figures are important… depending on your audience. If you are in a chemistry class, chemistry lab, or writing a paper on something chemistry related, then yea, use those significant figures… But, if you want what you are writing to be understood by the normal person, (or in medicine where a missed decimal could kill someone), then always have the leading zero, and omit a trailing one.
In fact, some programming language parsers will accept either 0.5 or .5 as a numeric constant, while some parsers accept 0.5 but reject .5 – I forget which is which. I’ve recently dabbled with JavaScript, PHP, and (I forget what else) and ran into this somewhere. I think there were some inconsistencies about this among early Fortran compilers. I think Pascal rejected .5 also. (And I’m not sure, but there may have been some rule that real constant required at least one digit to the right of the point, i.e., 5. was wrong but 5.0 was okay.)
Rule of thumb: If you have to deal with multiple languages without your head exploding, just get in the habit of ALWAYS writing at least one digit on each side of the point.
I never ℓearned this in schooℓ, but I picked it up somewhere, many years ago. I’ve ℓong been in the habit of writing ℓ for ℓower-case eℓℓ pretty much everywhere I ever need to write ℓower-case eℓℓ, particuℓarℓy for any kind of technicaℓ appℓication or context.
Thus, we would have composite measurements like: 3.456 m question[sup]2[/sup] / block cow[sup]2[/sup]
ETA: Or, alternatively written, 3.456 m question[sup]2[/sup] block[sup]-1[/sup] cow[sup]-2[/sup]
While I agree in general with the spacing rule, I think that looks weird. Degrees (°), along with minutes (’) and seconds ("), are not units but fractional indicators*, like the decimal point. Thus they come right after the number.
And the unit comes right after the symbol, for some reason that I do not know. Maybe the space under the symbol is considered to provide enough visual space.
*I think they are also locational indicators, hence why one has degrees Celsius but merely kelvin.