A long, long time ago, homo sapiens started measuring things. The units of measure were of course pretty practical and diverse: Distance between home and the girlfriend's cave might be measured in days of walking, long times might be measured in moon cycles, weights in what a man could carry, and so on. It worked, sort of. Not very precise, but good enough.
Over time, countless more or less standardized units emerged. Many of these were based on the homo magnus principle: The bodily dimensions of the ruling king were the measure of all things! Feet, braces, inches, spans are example of this. Of course, clever businessmen with large feet and a petite wife often tried to sell by their wife's feet and buy by their own feet, until the king distributed sticks sized to his very own royal feet and told people to use these, or else…
Of course, the king could not avoid that another king at another part of the world used HIS feet instead. The Chinese foot is nearly 10% larger than the American version, while the official foot in Hong Kong is even larger, by almost 22%! Would you have imagined that? It seems that shorter people have larger feet! Anyway, we ended up having a myriad of different units to measure the same things. Some of these units were known over larger areas, others were extremely local. The local ones were no big trouble, but rather the trouble lay in those units that pretended to be worldwide standards, but in fact were not unique! They came in different flavors and different sizes, and that REALLY can create confusion and trouble!
For example, the mile was invented by old Romans. The word comes from “mille”, Latin for “thousand”. It simply meant thousand double steps. Of course, Romans with longer legs would measure a different mile than the smaller ones. A child's mile might only be half an adult's mile. So it was standardized, but only to a point: Sailors apparently had longer legs than the landbound population, so that the nautical mile ended up significantly larger than the terrestrial mile! Or perhaps when walking on water they slip a bit and that makes their paces longer? Anyway, the longest legs were those of the Germans. Their mile was nearly four times as long as the nautical one!
Something similar happened with the gallon: The English version of it is significantly larger than the US one. They probably are thirstier. Or the ounce, but here the situation is the other way around: The British ounce is smaller than the US version! This leads to a gallon having 128 ounces in the US, but 160 ounces in the UK! Go figure how that came to be… And the best is that some people who use gallons and ounces day in, day out, don't even know this!
The ounce has a special problem: It comes not only in several sizes, but also it comes in totally different flavors! It's not only a measure of volume, but also a measure of mass… and as measure of mass, again it comes in several sizes: Even in the USA alone, there are two sorts of mass ounces, one of which is roughly 10% larger than the other! The Chinese mass ounce instead is much larger, almost twice as large as the smaller of the USA ounces. Such a situation creates infinite chances for misunderstandings!
Something even worse happens with the almud. This ancient arabic unit was brought into Spain and from there spread out over much of the Spanish-speaking world, but with extremely different meanings! It could mean a volume, but of greatly varying size. It could be an amount of cereal, measured by weight or by volume, and being three times larger in one country than in another. It could be even a surface of land, again highly variable in its dimension! Some countries at some point in their history standardized the almud, but there was never any agreement between the many countries using it. So, if someone wants to sell you anything specified in almudes, better be very careful! Your almudage might vary!
In history, units of mass have come in incredible variation. When people
came up with the idea of packing goods into tons, there was a long and
a short ton. Logically, the long one could fit a bit more merchandise.
Later, someone had the brilliant idea of using these tons as unit for mass!
Of course, it's crazy to use the appendix “long” and “short” for mass,
when these words really imply distance… but to this very day some stupid
people use them.
A particularly funny chapter is measurement of power. People love animals, and they specially love to make them work. So, power was often expressed in relation to the amount of it that could be gotten from common farm animals: oxen, goats, cows, horses, donkeys. Despite oxen being so very common as work animals, the oxpower never really became well known. Instead, the horsepower won as the most used unit, with donkeypower being a close second for some time, but later falling out of favor. Of course, horses vary in size and strength… and the world got several different definitions of the horsepower. The French even had a steam horse (cheval vapeur), if you can imagine such a thing, and this poor steam horse varied greatly in size: When it was used to specify the power of an engine for a sales argument, it was about the same size as an average non-French horse, but when it came to paying car taxes, which were calculated according to the amount of steam horses the car had, these poor beasts were inflated about 13-fold, by tricks even taking into account the shifts the car had. Imagine those poor blown up horses! Maybe that's why they called them steam horses? Because they were inflated with very high steam pressure, and after having paid the taxes, the steam could be condensed and the steam horse conveniently collapse again to a nice compact size?
I can understand that when Daimler built his first engine to be used on a vehicle, he rated it in horsepower, so as to give an idea how many horses that device could replace. After all, his vehicle wasn't much different from a horse-drawn cart! Same thing for a steam engine intended to replace horses at a British coal mine water pump. But it's beyond me how a pilot can feel comfortable thinking about his aircraft engine in terms of horsepower! I mean, 180 horses cannot make a Cessna fly!!! If at least the good folks at Lycoming would use pegasuspowers to rate their engines!
Heat power was measured in calories per minute, or British Thermal Units per hour, or any of many other measures. Of course, heat power or any other sort of power can share a single unit, and thus the power of a lamp or an engine could also be stated in these units! More confusion, because some people took for granted that a calorie was a certain amount of heat, while in truth it's a certain amount of energy of any sort! Moreover, since a calorie is a small unit and it's usually more practical to measure in kilocalories, some creative people came to call a kilocalorie a “large calorie”, and often shortened this simply to “calorie”! At least, that's what I was told by an editor from the National Geographic Magazine. I had a little fight with them over this issue, some years ago, when I complained about a factor 1000 mistake in their article about nutrition, and they told me they used the word “calorie” in its meaning of “large calorie”, which is in fact “kilocalorie”! Go figure, once again! I found their reply folkloric and extremely unsuitable for a pseudoscientific magazine, to say the least…
In any case, at the time the industrial age started, humanity had amassed a fabulous fortune in different, conflicting, error-inducing units, often with strange, funny or confusing names such as feet, knots, horsepowers, pounds, pennyweights, stones, atmospheres, lines, bars, minims, barrels, quarts, and so on. And the worst of all is that these units don't work together very well! In pre-industrial, simple life, this was no major problem, but when science really took off and became a household item, the lack of good interoperability between these units started to be a major drawback.
So, a new measurement system was devised. It was scientifically designed, using the best knowledge available, to be logical, perfectly standardized, reproducible, and highly interoperable so that scientific and technical calculations would not need conversion constants. This system was intended from the start to be a worldwide standard, to end once and for all time the measurement-related misunderstandings in science, trade and traffic. Even if you can't believe it, the system was developed by the French, the same crazy people who also came up with the inflatable steam horses!
The new system was constructed in a logical way, as far as the fuzzy human mind allows this. There was to be just ONE unit of measurement for every physical magnitude. For example, the unit for distance would be called the meter, and EVERY distance would be measured in it, regardless how large or small it was. Not like the stupid British system, where length could be measured in inches, feet, yards, furlongs or miles, to mention just a few of the many options! In the new system, for adapting to small and large distances, prefixes would be used that allowed to easily multiply the unit in decimal increments, from trillionths to trillions and much more! These same multipliers would be user for each and every unit. Only basic units, like distance, time, temperature would be freely defined. All derived units, such as speed, acceleration, inductance, would be built on top of the basic units. This is a fabulous advantage over every older system! You can simply multiply and divide any values in these units, to obtain the result in the correct unit of the resulting class. For example, one watt is the power that is required to free an energy of one joule in one second. This one joule is the energy required to push something with a force of one newton over a distance of one meter. The power of one watt means that the object will move that one meter in one second. This same one watt is the power defined by putting a current of one ampere through a resistor of one ohm, and the potential difference that will appear across this resistor is one volt! If instead you put this current of one ampere into a capacitor of one farad during one second, the capacitor will charge to one volt. Or if you apply this one volt to a coil of one henry, the current will rise by one ampere in one second. By the way, if the coil has one turn, then applying one volt to it for one second will result in a magnetic flux of one weber, and this flux distributed over one square meter of area is of course a flux density of one tesla! Everything is one by one by one! What could be easier than this? No other measurement system ever in history has been as practical! Every other system requires conversion constants in most or all of these calculations!
It stands to reason to think that scientists, engineers and technicians really ran to embrace this new, excellent, highly practical system! And so it was. But convincing their governments that the new system should be used for everything, was a slower process. France, the country where the system was developed, was of course the first to make it the main, prime, and only system in use, in 1795. It took decades before finally other countries followed, but then a steady landslide set it and over the years almost all countries passed laws that made the SI, as this system was simply called after its French full name, the one and only system in use in their territories.
Around 1950, the world was divided basically into two bands: The larger part of it, including most of Europe, South America, and much of Asia and Africa, were officially 100% metric. This didn't mean that no old fashioned units were used anymore at all, but it meant at least that every official contract and publication would use the international standard, and this made the metric system permeate all levels. England instead, together with its current and former colonies such as the USA and Australia, were only lukewarm about the system, accepting it as valid and convenient but not making it compulsory. As a result, in these countries science worked mostly with metric units, while daily life still used the shoe size of a long perished king to measure things! At the same time, a number of underdeveloped countries had not really looked into the issue more closely, and so had an immense range of ancestral, variably sized units in daily use.
During the second half of the 20th century, one after another of these diehard inchpounders and almuders fell. Some did it with firm decision, by passing a law that simply said that from this date on, everything has to be measured in SI units and that any other unit is illegal. A quick blow certainly hurts less than a slow agony! But the UK and its group of colonies were so tremendously attached to their beloved illogical units, that they took the change very slowly. Some of them stretched the conversion out as long as possible, living in a dual system with everything specified in one old and one new unit. That's very awkward, and it was not helped by the fact that politicians fought bitter wars over the all-important issue of whether the inches had to be stated first and the centimeters in second place, or if it had to be the other way around! It was a good show of homo stupidus in action.
Right now, 2006, the world definitely has accepted the SI, with just one single important player that still stubbornly rejects its full application: The USA. They are in the good company of two much smaller players, Liberia and Myanmar, which haven't officially legalized the SI mostly because they have more pressing matters to care about, or too little scientific knowledge to even worry about measurement! That might be fine for them, but I just plain simply cannot understand why the USA, which until not so many years ago was an extremely progressive and open-minded country, pushing for technical development and actually leading it, could fall back so much that it has become the very last of all industrial countries in the world still clinging to a totally obsolete and completely hopeless system! It's not that there haven't been attempts: Specially in the 1970s, the USA was seriously on its way to adopting the SI, but then stupidly hit the brakes and steered back!
In 1999, the USA made the entire world laugh and cry at the same time, when the Mars Climate Orbiter crashed because two USA companies, which made subsystems for it, had failed to agree on using the same units for the intercommunication of their modules. Lockheed Martin gave a value in pounds of force, Jet Propulsion Lab thought that newtons were meant, and the result was a new impact crater in poor old Mars, who had absolutely no guilt in it! This case illustrates that a slow, insecure move from one system to the other, with long co-existence of the two, is dangerous and problematic. If the move to metric in the 1970s had been completed as planned, this costly, embarrassing and widely publicized accident would certainly have been avoided!
It's obvious that most people don't like being told to give up something they have used for all their lives, and instead switch to a completely new system, which they first have to learn. This reluctance to change is very natural, anchored in the way the human brain works. But when the proposed new system is so very much better than the old one, reason should win over mental inertia! The USA's population has not been slow to adapt in other fields. They have accepted cellphones just like the rest of the world, they have converted mostly to DVDs and left VHS tapes behind, they have embraced computers and the internet even more than most countries, and this list could be lengthened at will. So, why does the US government think that its population is not willing to move on to a better system of measurement units?
I have a lot of daily contact with people from the USA, and I love kidding them about their absurd and obsolete measurement units invented by their former colonial bosses. My feeling is that most USAmericans do indeed have some trouble moving away from the accustomed mess and on into new, logical and clean measurement territory, which they not always see as being that, but that they do see the advantages and are mostly willing to do the change. So, why hasn't it happened?
In fact it is happening. More and more people from the USA know how to use the SI, and use it in the technical fields, while they keep using the old units in daily non-scientific life. But wait a moment! Everyone in the USA uses the metric system in certain fields where the old “customary” system simply has no units! For example, everything electrical in the USA is fully metric. They measure electric potential in the SI unit volt, just like everyone else in the world, and they even go so far as to speak about “voltage” instead of “potential difference”, “tension” or whatever! Talk about being ultra-metric! Their circuit breakers are rated in amperes, the power is rated in watts. But don't look too deeply into magnetics, or you will find USAmericans using the gauss and oersted, which are units that are neither part of the SI nor related to the inch-pound system. Basically, in every field they are using the oldest, most obsolete units they could possibly dig up.
It's beyond me why USAmericans use so many different units for power! It's totally crazy to see the specifications of a US-made air conditioner: Its electrical power is rated in watts, its mechanical power in horsepowers, and its thermal power in british thermal units per hour! Why on earth don't they use a single unit for all three powers? A German air conditioner instead would do just that. It would be rated, for example, at 1000 watts electrical power consumption, having a mechanical motor power of 800 watts, and a thermal power of 3500 watts. This allows to see at first glance that its motor is 80% efficient, and also that its overall efficiency factor, this all-important number for energy efficiency of such a machine, is 3.5. Instead, and air conditioner in the USA might be rated at consuming 1000 watts, having a motor output of 1 horsepower and a thermal output of 9000 british thermal units per hour! If you want to find out its motor efficiency, and its overall efficiency factor, you need to dig up the definitions of the units and get seriously into math!
Dear USA, please find your way back to your proud history as a modern
country, and embrace the better measurement system already used in the
rest of the world! After all, do you know what the present definition for
an inch is? Well, it's nothing other than 25.4 mm! Yes, the inch is defined
in terms of the metric unit! So, instead of using the metric system in
a hidden and indirect way, why not use it openly?
No, no way! The SI is not a perfect system. It's actually far from that! It has many inconsistencies and lots of room for improvement. For example, I find it inexcusable that the kilogram was selected as basic unit of mass! “Kilo” is a prefix, and should never be part of a unit! So, in the spirit of the SI, we should really have to add a second prefix when we need to measure large or small weights. A big bug might then weigh a millikilogram, but no, they tell us to simply use the gram in that case. This stupid use of a prefixed thing as a base unit is doubly inexcusable, if we consider that when the system was defined, there was an actual non-prefixed base unit for mass, the grave, equivalent to a kilogram and symbolized by an uppercase G, but shortly later, due to the whims of a king, the grave was buried and replaced by the kilogram!
Another illogical matter in the SI is the use of uppercase or lowercase
characters for the symbols and prefixes. As it is now, the unit symbols
are uppercase when they are derived from a name, and lowercase otherwise.
The prefixes are uppercase from the mega upward, and lowercase from the
kilo downward. This is silly! It would have been much better to invent
a system where all unit symbols are uppercase and all prefixes lowercase,
for example. If there was absolutely no way to avoid a mix of uppercase
and lowercase prefixes, the logical thing would have been to write all
prefixes that multiply a unit in uppercase, and all that divide it in lowercase!
But no… the line was drawn between thousand and a million, rather than
Another unfortunate feature is using the same letter, the lowercase m, both for milli and for meter! Sure, when I read mm I know it means millimeter and not millimilli nor metermeter nor metermilli. But when I read ms, how can I know if it means millisecond or meter second? Both make sense! Well, I have to look very closely, because if it means meter second, there should be a tiny space between the m and the s. But that space might not be very obvious, and so I might have to go guessing from the context. That's not nice. Guessing should have no place in a measurement system, nor should a tiny little space be used as the only differentiation between two totally different things .
As it is now, one has to be really careful about the use of uppercase and lowercase letters. You can rate a power in kW, which means kilowatt. If you instead write KW, as many people mistakenly do, that strictly means kelvin watt, and is something entirely different! Many people haven't noticed this, and write their symbols the wrong way.
There are several more such problems in the SI, and I hate them. Still, with all its problems, the SI is by far the best system of measurement units we have, and as long as no better one is defined, everyone in the world should use the SI.