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Old 2021-09-28, 14:55   #1
Uncwilly
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Default Philosophy of units of measurement

My automobile has the option between English measurements (mph, mpg, mile [range and total distances]) and French (kmph, /100km*, km [range and total distances]).
kmph vs mph makes sense, as the conversion is a direct multiple by a conversion factor.
miles vs km also makes sense for the same reason.

But then comes /100km vs mpg [ymmv]. They have a difference in philosophy, as they are inverse from each other. The one focuses on how much fuel one uses for a set distance (so one knows how much one needs to get to their destination), lower is better. The other focuses on how far per unit of fuel (so one know what distance one can expect when they fill their XX volume tank), higher is better.

Why are these different (why the English system doesn't use gallons per 100 miles or the French system doesn't use kmp?
Which one is more practical for the average person?
Which is better (your opinion)?
What other measurements in broad, common usage (aka consumer level) show differences of philosophy like this?
Let's wait until October to discuss the units like this that are used by the technical crowd.

* Am using so that it does not get mistaken for 1 or I based upon font.
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Old 2021-09-28, 15:51   #2
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There is also wire gauge, which gets bigger when the diameter of the wire goes smaller. For me as a person with metric background, it was quite misleading until I looked it up because a video I watched would not have made sense at all otherwise.

So there are certainly more examples like this.

In my family, we use l/100km, only because we are used to it. I'm sure something like km/l would lead to confusion and that the other unit is "better". That's like my grandparents who liked to calculate all prices in DM because it was "better" (in reality, they had a better understanding on what's something's worth in DM, because they used that as their currency for decades). So I guess it's largely a matter of what you are used to and if you are willing to adopt or learn something new. Especially my non-natural-science-savy family members would have problems understanding why you could "invert" the unit. But personally I like the approach of mpg.

I guess I do not get the joke why we would need to wait until October? Metric vs imperial calendar?
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Old 2021-09-28, 16:16   #3
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Quote:
Originally Posted by kruoli View Post
I guess I do not get the joke why we would need to wait until October? Metric vs imperial calendar?
No joke. I was just hoping to give space for the units that the person on the street would use. There are plenty of technical units that are inverse or have particularly odd unit (like our favourite Ghz-days/day).

I just thought of another (pair of) unit(s) that is gaining common usage that are a different philosophy than another commonly used unit. km or mile per hour is now becoming a common reference with regard to electric vehicle charging rates. This is as opposed to % of total charge per hour.
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Old 2021-09-28, 17:13   #4
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Quote:
Originally Posted by Uncwilly View Post
My automobile has the option between English measurements (mph, mpg, mile [range and total distances]) and French (kmph, /100km*, km [range and total distances]).
Strictly speaking, and one should always speak strictly especially to animals and small children, it is not a French unit. It is commonplace throughout Europe at least. Much the same can be said about "English". It is ubiquitous in Scotland, Wales and Northern Ireland at least.

I always think in terms of mpg but recognize that is ambiguous. The North American colonists have strange ideas about the size of a gallon.
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Old 2021-09-28, 17:17   #5
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Quote:
Originally Posted by Uncwilly View Post
No joke. I was just hoping to give space for the units that the person on the street would use. There are plenty of technical units that are inverse or have particularly odd unit (like our favourite Ghz-days/day).

I just thought of another (pair of) unit(s) that is gaining common usage that are a different philosophy than another commonly used unit. km or mile per hour is now becoming a common reference with regard to electric vehicle charging rates. This is as opposed to % of total charge per hour.
The metric unit of fuel consumption is square-metres in SI units.

(Litres are volumes, approximately 0.001 cubic metres; km are -- rather obviously --- lengths.)

I guess that the Imperial equivalent is inverse square yards.
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Old 2021-09-28, 17:38   #6
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Quote:
Originally Posted by xilman View Post
The metric unit of fuel consumption is square-metres in SI units.

(Litres are volumes, approximately 0.001 cubic metres; km are -- rather obviously --- lengths.)

I guess that the Imperial equivalent is inverse square yards.
https://what-if.xkcd.com/11/
Quote:
Gas mileage is measured in square meters.

You can even plug it into Wolfram|Alpha, and it’ll tell you that 20 MPG is about 0.1 square millimeters (roughly the area of two pixels on a computer screen).
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Old 2021-09-28, 18:06   #7
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Quote:
Originally Posted by retina View Post
Aw, I was thinking of posting this, too. Worth a read, especially because he gives an example of how to interpret an area in this context in the "real world".
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Old 2021-09-28, 18:10   #8
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Quote:
Originally Posted by xilman View Post
Strictly speaking, and one should always speak strictly especially to animals and small children, it is not a French unit.
The origin is French: https://www.metricmetal.com/history-of-the-metric-system/
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Old 2021-09-28, 21:30   #9
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Quote:
Originally Posted by Uncwilly View Post
* Am using so that it does not get mistaken for 1 or I based upon font.
This is a special case so you can use either lower or capital letter.
First chapter of Thermodynamics at any engineer degree in Portugal is about SI units and its prefixes.
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Old 2021-09-28, 22:24   #10
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Quote:
Originally Posted by pinhodecarlos View Post
This is a special case so you can use either lower or capital letter.
There are many special cases. Serious people should be aware of them all.

Quote:
Originally Posted by pinhodecarlos View Post
First chapter of Thermodynamics at any engineer degree in Portugal is about SI units and its prefixes.
Having gone through the whole Imperial to Metric transition as a young student in Canada, I understand the confusion well. Even the teachers didn't understand what they were teaching (and I found that they *really* didn't seem to enjoy being corrected when they were wrong...).

I was "all in" on the beauty of base ten units for all measurements (the French do do the theoretical extremely well).

I began to question my presumption that this was optimal when I started working with the "real world". People I was working with were able to "fold" fractions in their heads, almost instantly and exactly.

As Musk recently said, "A pascal is what? A mouse fart?
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Old 2021-09-28, 22:51   #11
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I would had said Pascal instead of pascal.
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