I was walking through the metric jungle

Today was a wonderfully sunny day, so I said to myself, “Hey, why not take a stroll through the metric garden.”  (Why do I ask myself such things? Don’t ask me.) The metric stroll should be easy enough, with its scientifically simple base ten measures.  The simple meter is wonderfully divided up into 100’s and 1000’s for convenient lengths of measurement.  It also quickly multiplies into…umm, kilometers.  No one uses hectometers? Oh wait, the French kind of do to derive their hectare.  It’s funny, that hectare isn’t listed in SI.

It’s arbitary

Sure, the imperial foot may have been based on someone’s actual foot length, but it is a useful length for some industries. Its not nearly as arbitary as the meter, which is defined as the distrance that light travels within a vacuum in 1/299792458th of a second. Why does SI use a bizarre fraction to define the core unit of measure for their decimal system?

Maybe base ten numbers aren’t all they are cracked up to be. What, never heard of metric foot? Or for that matter, metric ton, metric inch, or metric mile. Why do all of these units exist? For all the berating that the imperial system gets, the measures within it are based on real world needs. Since ancient times, units very similar to the modern imperial system have been common place. That said, it may be important to note that both SI metric system and imperial system have goofy offshoots.

Missing units!

Hey, what happened to the liter? An entire unit of measure for volume is missing from the international standard! Did aliens abduct the liter for use on their alien world? Well, no. It’s actually very common in the US, if that doesn’t seem ironic. Oh, and don’t get diehards started on a discussion about the correct spelling of meter or liter!

Psst, USA is metric!

Something else that is ironic, the USA has been legally metric since 1866.  So, it’s not true that the USA isn’t metric.  Neither is it true that the rest of the world is 100% metric.  Specific industries, companies, populations and individuals still have the right to choose their standards and measures, both in the USA and elsewhere.  Pipe threads in France are NPT, not the ISO sizes that were meant to replace them.  Pints of bitter are still actual pints in Britain.  Speaking of Britain, I’m reminded of the TV show Top Gear.  Miles, horsepower and inches are so commonly used on that show, I forget that the UK is supposedly metric.

This stroll through the metric garden is starting to look more like a forced hike through the metric jungle.

8 thoughts on “I was walking through the metric jungle

  1. Pat, cute article. I won’t be one to promote the boyscott of metric goods. Just a bit put off by the promotion of the metric system as some sort of de facto superior system. Units of measure are arbitary, and the metric system is no exception. Some stuff is easier in metric, some stuff is easier in imperial…and the rest just doesn’t really matter all that much. Is my life really different because my toothpaste is 5oz instead of 140g or .15L or is that .15l? 🙂

  2. I would like to know your thoughts on compliance with ASME Y14. I work for a 75 years old company that will be increasing its global manufacturing presence with our sister companies and outside vendors. Part of this process was a review of our current drawing standards. We purchased 13 standards (Y14.1, 14.2 etc) and after a six month review, I discovered that we are not in compliance per the standards. The discrepancies vary but the drawings generally comply with accepted drawing conventions. One of the biggest points is our use of symbols. For example, we use a triangle with a number for revisions instead of the supported circle with a letter. There are many other examples but that should suffice as an illustration. I would like to know if you see this as a rigid set of documents that must be adhered to in all aspects or a general guideline that you can pick and chose. Most 3D CAD platforms don’t follow all of the conventions shown in the standard anyway (i.e. section through a rib). Does anyone follow this set of standards to the letter, and if not, to what degree do they deviate? The issue of appropriate application of GD&T symbols (Y14.5) is a whole other issue and separate from the internal debate. Half of the department wants to make the change and the other half change only what is essential as being 100% compliant would take thousands of man hours redrawing our most used drawings all the while we are in the midst of a PDM implementation. I would like to see a wider discussion of this topic and see others perspective.

  3. The metric unit of length is not arbitrary (the distance that light travels in a vacuum is just an accurate and repeatable length to compare it with. Metric length is linked by design to the metric units of weight and volume. A cubic decimeter (or liter) occupies a volume of 10×10×10 centimeters. Also, one liter of liquid water has a mass of almost exactly one kilogram.

  4. Metric is extremely arbitrary. It was originally based on one ten-millionth of the distance between the North Pole and the Equator. Of course, this original definition was flawed because the shape of the Earth isn’t a perfect sphere. Definition was later changed to something more reliable, but still just as arbitrary. This is how we ended up with the near ludicrous 1/299792458 number. The meter is the post-child of arbitrary units, being based on nothing practical for purpose to which it is to be used. Does it work? Yes. Is it simple to do math with it? Most (but not all) of the time. But it’s still arbitrary. Original authors could’ve used a much less arbitrary standard as the definition of the meter, but chose to use flawed concepts about Earth as their basis.

    The liter itself, it is accepted by SI, but it is not an SI unit.

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