Dragging America Into the 20th Century

“?There are two types of nation” a recent Nature editorial begins; “…those that use the metric system and those that have put a man on the Moon.”

Such a pro-American jingoistic statement must be deep British irony. Anyway, the editorial continues …

The reliance of the United States on feet and pounds, along with its refusal to embrace metres and kilograms, baffles outsiders as much as it warms the hearts of some American patriots. But it is time for the country to give up on the curie, the roentgen, the rad and the rem.

This is about measuring radiation. There are several ways of measuring radiation. This has to do with the different ways radiation can exist, and the different kinds of effects it can have. For example, one might want a measure of biological damage, in order to measure, control, document, and discuss exposure in work places or disaster sites. The American tradition for this particular measure is the “rad” but by a 1970s convention that the US apparently ignores, it is the sievert.

The editorial points out the confusion, sometimes meaningful confusion, that arose in the wake of the Fukushima multiple meltdowns, when the Europeans and the Japanese were using sieverts and the Americans all had to pull out their slide rules to convert between sieverts and rads in order to keep track of what was going on. The Nature editorial notes,

Yes, it is possible to use both sets of measures, and to follow the rem numbers with the sievert numbers in brackets. In practice, this is what many US regulatory agencies do. But it is simply too awkward. The Australian government has publicly criticized the US system for creating confusion.

In the middle of an international nuclear-radiation incident, should emergency-response officials huddled in a situation room really need to whip out their calculators?

As I was reading this editorial, I recalled the space robot that essentially crashed into Mars instead of falling into a nice orbit, because the American part of the team was not using the SI (International System of Unites) method of calculating the movement of the robot’s mass. It seems that confusion over units could cause much worse disasters than losing a single (and expensive) robot.

The editors of Nature had the same thought.

Remember NASA’s Mars Climate Orbiter, which was lost in 1999 when someone forgot to convert between imperial and metric units (even though they had plenty of time to check) — the spacecraft broke apart in the Martian atmosphere rather than smoothly entering orbit. Imagine if such an embarrassing error involved the life and safety of millions of people here on Earth.

Clearly, they have a point. The US nuclear industry resists this change because, they say, of cost. However, as Nature argues, it is already the case that the companies that manufacture equipment (and I’d guess software) for use in the nuclear industry already use both units, since they tend to be international.

The US should do this, and should go metric.


  1. #1 Doug alder
    September 20, 2016

    Given that it seems there is a better than distant chance that your country is about to elect a complete anti-science psychopath as President all I can say is good luck trying to convince the rest of your citizens to switch to metric.

  2. #2 Esa Riihonen
    September 20, 2016

    As an European physicist – YES! 🙂
    As a physicist – a nit pick. 🙂
    The SI measure of biological effect is Sv (sievert) the corresponding “American” unit is rem – not rad.
    The SI counterpart of the rad is Gy (gray).

  3. #3 Christopher Winter
    September 20, 2016

    I have long hoped for this to change in the U.S. It has changed in a few places. Wine and liquor, for example, are now measured in liters. But those are the exceptions.

    And isn’t it passing strange that a country which has pushed globalization so strongly for the past several decades should continue to resist signing on to the only global system of measurements?

  4. #4 Brainstorms
    September 20, 2016

    Chemicals are metric. Industrial gasses. Aerospace engineering is metric. A good percentage of the fastener industry make metric nuts & bolts. Etc.

  5. #5 Brainstorms
    September 20, 2016

    NASA’s Mars Climate Orbiter, which was lost in 1999 when someone forgot to convert between imperial and metric units…

    Credit where it’s due: Lockheed Martin was still in the stone ages and gave NASA avoirdupois measurement units in a metric arena.

    The interface specifications they were in possession of specified metric units. They ignored that, and the engineers at JPL who (were using metric units and) caught the discrepancy were not listened to by their management…

  6. #6 Eric Lund
    September 20, 2016

    I have vague recollections that the US was about to go metric sometime in the latter half of the 1970s. We got one- and two-liter soda bottles, and as Christopher@3 notes, 750 ml bottles of wine and distilled liquor. That was it. If anything we have been backsliding: road signs that were once posted in both miles and kilometers are now posted in miles only.

    But it apparently had a bigger effect north of the border. I am told that Canada switched to the metric system specifically because the US was about to switch to the metric system.

    Here and there you will find remnants of the old system even outside the US. The UK still signposts roads in miles, not kilometers. In Canada, even in Quebec, land is sold by the acre rather than the hectare. And there are are historical references in many places, e.g., China’s Ten Thousand Li Long Wall (most English speakers know it as the Great Wall), which is actually closer to 13,000 li long (the li is a historical unit of length in China, a bit short of 500 m). But outside the US, these are exceptions. Only in the US is 32 degrees associated with ice; elsewhere, it’s a warm or even hot summer day.

  7. #7 Brainstorms
    September 20, 2016

    Canada switched around 1982, I think. It would have been best if manufacturers standardized on metric sizes, and put the fractional non-metric equivalents in parenthesis. That would have led people to adopt it, I think. They never did this, except in a few cases, such as soda bottles.

    You can hang this whole snafu on Congress. In the 19th Century, they made switching “voluntary”. Code-word for “Ha-ha, it’ll never happen and we’ll help you avoid it.”

  8. #8 Greg Laden
    September 20, 2016

    Esa, see? Confusing, isn’t it!

    Eric, Metric, 10 times better!

    Congress made an edict, an organization was set up, Schools started teaching it in preparation for the transition. It wasn’t going well by the end of the 70s because there was no mandate, then Reagan killed it. The evil Lyn Nofziger had a hand in it.

    The Soviets, after all, were metric.

  9. #9 Greg Laden
    September 20, 2016

    Another possible example of the Imperial-Metric problem for Space Robots:


  10. #10 Brainstorms
    September 20, 2016

    I think I was confusing the 1866 U.S. law that made metric system measurements legal, but did not mandate them as a national standard to replace imperial units.

    The U.S. Metric Conversion Act of 1975 encouraged the conversion to the metric system, but it was made voluntary — and so was stillborn.

    Canada’s conversion was a drawn out affair, occurring throughout the 1970’s, with most things metric by 1977.