By - klystron
I got lucky because I was in school before Reagan killed the Metric Conversion Act and so I was taught a thorough understanding of metric and SI units.
So, how complete and thorough was the teaching? Can you give some examples of how you were taught?
I was taught the SI prefixes, the metric base units, and how some of the base units were related to others. What I remembered most were the SI prefixes in the middle range and how easy it was to convert between them. I thought it was odd (and still do) that people use centimeters but not decimeters, and kilometers but not decameters and hectometers, which are perfectly valid units. A hectometer is about the size of a US football field if you include part of the end zones. I don't remember much about the actual lessons.
About the only lasting impact of the Metric Conversion Act I can think of is that in the late 1970's soda started selling in 2 liter bottles instead of 2 quart bottles. But I actually bought gasoline one time that was sold by liters instead of gallons in a rural Kansas gas station.
> What I remembered most were the SI prefixes in the middle range and how easy it was to convert between them. I thought it was odd (and still do) that people use centimeters but not decimeters, and kilometers but not decameters and hectometers, which are perfectly valid units. A hectometer is about the size of a US football field if you include part of the end zones.
Don't you also think it is odd that people don't use megametres, gigametres, millimetres (except in industry) or even micrometres or any other applicable prefix? Micrograms are common in medicine. There really is no use for the 4 inner prefixes. They are just hangovers from the original metric system and are not recommended for use in most disciplines. It works best and reduces clutter when the prefixes are limited to increments of powers of 10^3.
It was unfortunate that the switch to litre pricing at the pumps due to the price exceeding a dollar a gallon and half-pricing didn't last.
Millimeters are pretty common for things like wrench and bullet sizes. Gigameters and megameters should be used a lot more than they are although gigameters can only be used for outer space. The terameter is my favorite unit.
>It works best and reduces clutter when the prefixes are limited to increments of powers of 103.
I think hectometers and decameters are suited for everyday use. It's faster to say "a hectometer" than "a hundred meters". And a hectometer is just as useful as a centimeter which is very common. A decameter is a football 1st down and a hectometer is the whole field. I assume the 10^1 and 10^2 SI units are there because they can be useful for everyday experience.
Millimetres are very common in all aspects of industry, The centimetre is not accepted. Hun-dred me-tres is 4 syllables and hec-to-me-tre is also 4 syllables, neither is faster to say. I accept the inner 4 prefixes for defining certain other units, like the hectare and litre, The same can be said for pricing per 100 g versus per hectogram. I'd rather see schools teach the entire prefix series than just focus on the original series. They served their time, but we have moved beyond their need.
Personally, I think it helpful to look at the "inner prefixes" (milli- to kilo- inclusive) as a largely separate entity from the "outer" ones. The inner ones have little *scientific* application, but I can see plenty of useful examples of common usage.
Here's a big one: a runner with a record of 15.2 in the 100 m event cuts his time down to 14.9. How much did he improve? 0.3 second, right? Some might say "point three seconds", but I feel that that sounds kind of weird for values less than one. "300 ms" is valid, too, but not intuitive because of the absence of the extra zeroes, and it may imply false precision. Times are only measured to the tenth in this scenario.
Formally, it would be read "three tenths of a second", and "three deciseconds" is really just an easy, concise way of saying that. I use that style regularly, but there are other common instances of inner prefixes, too--height is measured most commonly in centimeters (though I do dislike the usage "173.4 cm"; just use millimeters if you're not rounding), air pressure is in hectopascals (a holdover from the millibar, I know, but it still helps to have whole numbers), land area is measured in hectares (square hectometer), which is derived from the are (square decameter), and that's not even mentioning the liter, which is just another name for the cubic decimeter! Deciliters and centiliters are also common, and the especially-common milliliter is equal to the cubic centimeter.
So yeah, perhaps they aren't *necessary*, but they are nice to have. It's the same rationale behind decades, centuries, and millennia. I also assume that this difference in use is the reason why deca has a double-letter prefix, which I imagine the common grade-schooler would prefer, yet micro resorts to a Greek letter, which scientists would prefer. Also note that all inner prefixes are lowercase--I feel it's just easier and more intuitive when you don't have to worry about casing. ("d" vs "da" is probably easier to teach a grade schooler compared to "d" vs "D", and then there's the whole milli/micro/mega fiasco...)
Yes, the inner prefixes do have limited usage, mainly for defining square and cubic units, like the hectare and the litre. The centimetre is also valid for height and clothing sizes. It's use becomes less useful, when decimal parts are included and thus the millimetre is more suitable. But, like the rest of the prefixes, there is a right time and place for them. They should not be used to the exclusion of the proper prefix.
Expressing 0.3 s as 300 ms implying false precision. False precision comes into play when a unit is converted and an over-precise value is used because that is what the calculator displayed. For example, if someone told you that something was about 6 miles away and that was converted to 9.656 064 km. Even rounding it to 9.6 or 9.7 can be construed as over precise when 10 km works just fine when the distances is known to be "about".
Claiming one is more intuitive than the other is a personal bias. Just like saying 1.75 m is more or less intuitive than 175 cm.
Perhaps it is a personal bias, and I wouldn't be opposed to seeing the unit symbols D, H, and K adopted to replace da, h, and k. The "da" has proved particularly troublesome for certain textbooks--I know that in school I was actually taught the abbreviation "dk", after the disgusting and inconsistent "American" spelling "deka-". (I'll accept "meter" and "liter"; that fits how we spell words like "center" and "theater". But "deka-" just looks archaic, is inconsistent with words like "decade" and "decathlon", is also inconsistent with "hecto-", and both spellings are accepted American usage according to Webster and OED. In fact, according to Google search trends, "decameter" is actually more popular than "dekameter", though only marginally.)
I can see the case for discouraging these prefixes, and I'm not suggesting we bring back "myriameter" and the like (we don't count in myriads, and haven't for a long time; however, we still count in tens and hundreds). But I don't think they're entirely useless, and I don't support pushing them into complete obsolescence. I actually might support a compound prefix exception to allow either deca- or hecto- to be used (only once) before a larger prefix to denote a factor of 10 or 100 (for example, "decakilometer" for 1000 meters, symbol dakm), and a similar rule for deci- and centi- on smaller prefixes ("centimilligram" for 1/(100 000) gram, symbol cmg)...but maybe that's more complex than it needs to be.
I don't know. Teaching "mega" and "micro" directly alongside the inner prefixes doesn't really seem right, due to the abrupt jump that might make a kid think that "mega-" means "10 000" and stuff like that. Also, "Dm", "Hm", and "Km" just look a little funky, and it might encourage more people to incorrectly write stuff like "KM" and "KG". Scientists can deal with such anomalies, and that's where the outer prefixes are primarily used.
I'm with you on one point, though: stuff like "3e9 km" annoys me to no end. Just say "3e12 m", or just "3 Tm". I'll accept such anomaly usage for kg (the base unit) as well as g (which makes finding the associated prefix easier), but there's no good reason to use km that way. Just promotes the false idea that meters-to-kilometers is a unit conversion, when it's really just the same unit with an internationally-agreed-upon numeric factor word.
> Perhaps it is a personal bias, and I wouldn't be opposed to seeing the unit symbols D, H, and K adopted to replace da, h, and k.
I agree and the prefixes hecto or hekto and kilo should be changed to hecta or hekta and kila. This would make all of the multiple prefixes two syllable ending in a. Will it happen? no.
>(I'll accept "meter" and "liter"; that fits how we spell words like "center" and "theater".
You'd better look around. There are some shopping centers that use the spelling centre in their name and theatre is as frequent than theater. In fact, a theater is supposed to describe a place to see movies and a theatre is where live performances are viewed.
If Americans can handle centre and theatre they can handle metre and litre.
> don't know. Teaching "mega" and "micro" directly alongside the inner prefixes doesn't really seem right, due to the abrupt jump that might make a kid think that "mega-" means "10 000" and stuff like that.
Wrong. All of the prefixes need to be taught. This is why SI is incorrectly taught everywhere. Only the old prefixes get a notice, never the expanded series. Because of this counting words are added between numbers and units that no one can really comprehend. The numbers become to large to handle. The prefixes were invented to make understanding of dimensions simple.
It may not work to teach the higher level prefixes to young children. They can learn them parallel to the equivalent counting words. But taught that prefixes replace counting words when applied to measuring units.
>I'll accept such anomaly usage for kg.
The prefixes and the exponential series should only apply to the gram. Personally, I would like to see the kilogram renamed. Maybe the BIPM should have a contest and request submissions for a new name. I don't know if the original name grav (pronounced as graf) could be resurrected or maybe gauss. The symbol would be G. I would prefer bar as a unit for mass. The symbol would be b. Bar is an old metric unit of pressure but it is not an SI unit, so there is no conflict. I have no problem with using deprecated cgs unit names for use in SI. Using them would help end their continued use in some fields.
There is only one unit for measuring distance and that is the metre. Kilometre, exametre, picometre, etc and not separate units. They are just prefixed base units.
Yeah, Americans do use "centre" and "theatre" on occasion, but mainly as a stylistic choice. They're commonly spelled "center" and "theater", and I feel "meter" and "liter" line up pretty well with that. There has been a distinct American preference for the -er spellings for a long time, so I don't mind that so much. That's not to say I wouldn't accept the international spellings, though, and ultimately, I don't really care about such things too much. The spelling "deka-" just bothers me, though, as there is no distinct preference for it (unlike NIST seems to claim), it's grossly inconsistent with other words with similar prefixes, and it just looks archaic. (In general, I would support a movement to make BrE and AmE spellings consistent, even if we were the ones to change, but it doesn't seem like any such movement really exists.)
And yes, I do believe that all prefixes should be taught in school, or at least from "pico-" to "tera-", but I think sticking to the inner prefixes is best when introducing younger children to the metric system. Science classes dealing with larger and smaller values should definitely put more emphasis on the outer prefixes and less on the inner ones (aside from kilo- and milli-). There are different levels of learning, and the SI is no different.
The kilogram thing is a weird inconsistency but it is also a long-standing status quo that is unlikely to change. When trying to calculate things like force in newtons, which uses kg rather than g, it can be useful to have the kg value given directly.
And yes. Meters to kilometers is not a unit conversion, and neither is any similar prefix change. But unfortunately, at least in America, there seems to be this general idea that it is, and because of that words like "hectometer" or "megameter" might confuse a lot of people.
> Yeah, Americans do use "centre" and "theatre" on occasion, but mainly as a stylistic choice. They're commonly spelled "center" and "theater", and I feel "meter" and "liter" line up pretty well with that.
As with centre and theatre, the spelling difference distinguishes the general meaning from the specific meaning as already seen with theater vs theatre.
The same is true with metre vs meter. Metre is a unit of length and meter is a device used to measure quantities. Ammeter, voltmeter, speedometer, thermometer, etc. The perfect example of this is micrometre and micrometer. Both have different meanings from each other and both are pronounced differently.
Micrometre is a prefixed unit and pronounce as my-crow-me-ter. Micrometer is an instrument for measuring small distances and is pronounced my-crom-e-ter.
Kilometre is a prefixed distance unit pronounced as key-low-me-ter. Kilometer has no meaning and is pronounced as kill-om-e-ter. This bad spelling results in the erroneous mispronunciation of the unit name.
Litre (lee-ter) is a unit of volume, liter (lite-er) is an alternate spelling for lighter, both pronounced the same way. You may also see here an example of the use of the word liter and how it is pronounced.
A limited teaching of the inner prefixes to the younger generation from a historical perspective may work, but these prefixes should not be used except for rare cases where they have a benefit. Mostly defining area and volume units.
The metric system (not SI) is taught as if this were still the 19-th century in a wishy-washy manner and the result is a lot bad usage, acceptance of errors and ignorance.
If Americans are confused by prefixed units like megametre and nanometre, it is no wonder they are in a high state of collapse.
From [BBN Times, 2022-05-13](https://www.bbntimes.com/global-economy/why-didn-t-the-us-adopt-the-metric-system-long-ago): An American economist discusses an article about the US's failure to adopt the metric system by Stephen Mihm, an American historian. (The original article is in *Business History Review*, Spring 2022, pp. 47-76, and requires a subscription to view.)
>We have now reached an odd point in the US experience where two measurement systems co-exist: the inch-based traditional system, along with pint and gallons, ounces and pounds, is how most Americans talk, most of the time, in ordinary life, but the metric system is how all science and most business operates (with the exception of the building trades). Many Americans step back and forth between the two systems of measurement every day in their personal and work lives, barely noticing.