In July 1983, Air Canada flight 143 ran out of fuel and had to make an emergency landing.
In September 1999, NASA lost contact with the Mars Climate Orbiter, its $200 million
spacecraft, after it crashed into Mars.
And in December 2003, a rollercoaster in Tokyo Disneyland derailed.
They all happened because of mix-ups between the metric and imperial systems.
Not pumping enough fuel, calculating incorrect trajectories,
and using an axle that was too small.
Pretty much every country in the world uses the metric system for measurement.
Having a universal system would be like having a common language across the world,
making it easier to communicate, trade and invest.
Well technically, it already has.
Yes, since all the way back in 1875 — and several times since — the United States
has committed to the metric system.
All its units have been defined in terms of metric standards since the late 1800s, and
it’s officially the “preferred system of weights and measures for United States
trade and commerce”.
Well, to understand that, we need to look back at how the metric system came to be.
For hundreds and thousands of years, humans used a variety of number and measurement systems.
Within the same country, you’d encounter different units while moving from town to town.
This obviously made things like trading a lot more complicated.
Fast forward to the French revolution.
At this point in time, France had tens of thousands of different standards.
The revolutionaries wanted, among other things, a radical new measurement system that would
be simple and universal.
People had already been developing a decimal system of measurement for some time, but the
revolution sort of sped things up.
The French turned to the constants of nature.
For example, the first definition of the metre was based on the distance between the equator
and the North Pole.
Other units in the new system were based upon the metre — one litre was defined as the
volume of a cubic decimetre.
And the system as a whole was decimal-based, to make conversions easier.
Like any widespread change, people didn’t take to it straight away.
They even abandoned it for a while before returning to it in 1840.
But the system soon became so useful that many other countries began adopting it.
A few decades later, an international agreement was formed to refine the accuracy of the standards.
17 countries signed the agreement, including the United States of America.
They declared the metre as the length of this metal pole, and the kilogram as the mass of
this metal cylinder.
85 years later, the metric system was updated again to bring it into modern times.
Known as the SI system, it established 7 base units.
This is the metric system as we know it today.
And in case you’re wondering, the metre is now defined once again by nature.
Anyway, getting back to the point, the US has signed several documents over several
decades, committing to the metric system.
So why is it still using the imperial system today?
The US Customary System, as it’s officially called, is not the easiest system to learn
— there’s no direct correlation between different units.
Instead of a decimal-based system, where units can be converted fairly simply,
there are several different conversions to remember.
But what’s interesting is these imperial units are already all defined in relation
to SI units.
Since 1959, the pound has officially been exactly 0.45359237 kilograms,
and a yard 0.9144 metres.
Which means even though everything you buy in the US is usually in customary units,
you can trace it all back to the metric system.
Also, the names for various imperial units are sometimes the same, which can be a bit confusing.
Do you think of the short ton, which is 2,000lb?
Or maybe the long ton, which is 2,240lb?
If that’s not confusing enough, these are just two of the several “tons” out there.
And if you’re sitting there thinking a tonne is 1,000kg, that’s the metric tonne, with
an extra “ne”.
The US has tried to switch to metric, though.
Several times.
Even though it was authorised for use way back in 1866, the strongest push for metrication
came more than 100 years later.
In 1975, Congress passed the Metric Conversion Act, and established the US Metric Board.
The board wasn’t given much power though.
It got as far as interstate 19 in Arizona, the only US highway to have metric road signs.
The board was then dissolved in 1982.
But then a few years later, the Act was amended to declare metric as "the preferred system”
in the United States.
Since 1994, both metric and US customary units have been required on commercial packaging.
And the metric system is now the standard in a lot of industries, with construction
being one of the exceptions.
But the reason it’s still not used in day-to-day life is because, while the Act has been amended
over the years, one key part hasn’t changed — the fact that conversion is still voluntary.
Other countries which have converted from imperial to metric, especially in the last
50 years or so, have successfully done so because it was compulsory.
In Australia, conversion to the metric system began in 1970 with some industries converting
first before others.
By the end of 1976, most industries and all packaged goods had been converted to metric.
Even the birthplace of the imperial system, England, began transitioning to the metric
system in 1965, to integrate more closely with continental Europe.
For them, it was a long and slow process.
There are still systematic hangovers from the imperial system, but in schools, the metric
system is taught.
These examples highlight the main reason most countries have converted, even when (not if)
faced with resistance — it’s to keep up with the global economy.
In the US today, only Federal agencies are required to use the metric system for business,
where practical.
While the US remains imperial, many private businesses are having to produce for both
the US and overseas markets.
Liberia and Myanmar are the only two other countries which haven’t officially made the switch.
But in practice, the two countries do use several aspects of the metric system in daily life.
It will take some time to switch over, and cost a lot initially.
But the cost of metrication is one-off, compared to the ongoing costs of servicing two markets.
So while the rest of the world continues to operate in a metric system, it seems like only a matter
of time before the US switches over.
Four of the 7 base SI units — including
the kilogram — are actually currently in the process of being redefined.
The definitions will return to fundamental constants of nature.
So no more metal cylinder.
So what changes will this have for you?
Not much.
Current definitions are fine for day-to-day use, but they’re just not up to scratch
for modern scientific testing.
So when the process is all done, you shouldn’t notice a difference.