| few notes: - "Fuel consumption of 9.4 L / 100 km" is not "the right form" is a modern take, a more classic and still valid SI one is km/l which is very similar to "Fuel consumption of 9.4 LPK"; - "25 {kW/h,kW⋅h} to boil a tank of water" are both strange forms, kWh is the common accepted way to express energy, no center dot multiplication needed; - multiple prefix (vs power-of-10) and bare prefix are as well commonly accepted, I see no reasons to consider them wrong, while I can state formally wrong "2 kilograms of rice" because we do not measure the mass but the weight so it should be 1.961daN where deca-newtons are commonly used because 1 daN is roughly 1kgf commonly shortened to 1kg as we can commoly count 1kg[f] == 1 daN... For instance climbing equipment in the EU use daN to express maximum loads of connectors, ropes etc because of that; - multiple quantities much depend on industry and conciseness, as we do not write units in table values but only in headers we tend not to write them three times in a row where from the context is clear what numbers means. The biggest issue is makes habits changes. Actually we should not use km/h as well, since for SI base unites are m/s, but 3.6 is not an easy conversion like kgf/daN, so in the EU we keep using km/h, something meaningful in the past, when we go by horses and feet, but not much needed today. Not to count software, where often recognize "°C" (two chars) BUT not ℃ (U+2103) and so on. |
No, it is the right form.
> a more classic and still valid SI one is km/l
The SI one has always been L/km. Any use of km/L is a translation over from mpg (miles per gallon).
> km/l which is very similar to "Fuel consumption of 9.4 LPK"
km/l is the reciprocal of LPK. These are not remotely the same unit.
> kWh is the common accepted way to express energy, no center dot multiplication needed
In SI, it is unacceptable to multiply units together without a space, dot, or cross. This can create ambiguities - for example, "mm" could mean "millimetre" or "metre × metre". "ms" could mean "millisecond" or "metre × second".
I had a discussion here a while ago where I changed from "kWh" to "kW⋅h": https://www.reddit.com/r/Metric/comments/1313rhp/how_to_resp...
> multiple prefix ... well commonly accepted
Not really. Other than saying "I drove 30 k km", it is rare to stack prefixes. We don't say that CPU features are "5 millimicrometres".
> bare prefix are as well commonly accepted
And this is wrong. So, I have this electric scooter that goes 80 k at 30 k and weighs 40 k. How do you like that?
> we do not measure the mass but the weight so it should be 1.961daN
Actually, it's possible to measure mass. If the scale has an internal reference with a known mass, then it can adjust to the local gravitational constant.
What I mean is, let's say an electronic scale has an internal 10 g mass. When switching on the scale, it measures the internal mass and sees 9.8123 mN (millinewtons). Now it will use that scaling factor for anything else measured during the session. Then you move the scale to the south pole, and it measures the internal mass to have a weight of 9.9765 mN, so it compensates correspondingly.
Likewise, if you use a balance scale, then you are comparing against known masses (not weights). (We'll ignore buoyancy for the vast majority of commercial applications.)
> For instance climbing equipment in the EU use daN to express maximum loads of connectors, ropes etc
I haven't been exposed to that before, so thanks for that. That's just about the only example I have ever heard of involving the deca- prefix. I would much prefer all the non-power-of-1000 prefixes to die (goodbye to centi-, deci-, deca-, hecto-) for many reasons.
> we should not use km/h as well, since for SI base unites are m/s, but 3.6 is not an easy conversion
Correct. I have used both km/h (because obviously society forces it) and m/s in various applications and calculations. Using m/s is much more helpful for visualizing distances traveled in a short span of time, and also calculating acceleration (in m/s^2, never km/h/s), kinetic energy, etc.