World Metrology Day 2020: measurement mishaps

This year’s theme for World Metrology Day is measurements for global trade. The aim is to “create awareness of the important role measurement plays in facilitating fair global trade, ensuring products meet standards and regulations, and satisfying customer quality expectations.”

Those of us in the quality business know that the difference between a functional and an unusable product can be a matter of microns. Obviously, we want everything to be 100% correct first time, but sometimes things can go amiss.

On the bright side, these measurement mishaps can provide valuable lessons about the importance of truly standardised measurement and attention to detail in quality.

Corrective eye surgery… in space

As you read this, the Hubble Space Telescope is circling the earth at around 17 000 miles per hour. The telescope might look like a child wrapped some tinfoil around a kitchen bin, but what Hubble lacks in looks it makes up for in brains.

Launched in April 1990, Hubble can see astronomical objects with an angular size of 0.05 arcseconds. According to NASA, this is like standing in Washington DC and being able to see a pair of fireflies in Tokyo that are less than 10 feet apart. Hubble uses this incredible precision to gaze into the inconceivably distant past, to galaxies 13.4 billion light-years away.

Even as someone who makes a living from writing, I’m not ashamed to say I can’t find words to adequately describe the awe inspired by images produced by Hubble. But the first pictures returned made space look pretty unimpressive…

Rather than unprecedentedly clear and detailed vistas of nebulas and galaxies, the fuzzy images suggested that the $1.5 billion telescope was somewhat short-sighted.

Engineers and opticians couldn’t improve the focus. The telescope’s 2.4 metre primary mirror was 2.2 microns too flat, which meant that light from objects of study was scattered.

As you can imagine, fixing a telescope the size of a bus in space isn’t the easiest job. In 1993, seven astronauts travelled 568 kilometres above the earth to the Hubble. To fix the error, the team fitted a Corrective Optics Space Telescope Axial Replacement (COSTAR) and a Wide Field and Planetary Camera 2 (WFPDC2).

Building and fitting the new equipment was an incredibly stressful and time-pressured situation for the team, carried out against the backdrop of a mocking media. But the first images returned after the fix were breath-taking. Hubble has since advanced humanity’s understanding of the universe with countless important discoveries.

A metric mix-up

Although most countries have officially adopted the metric system, other measurement units are often still used in the everyday lives of people around the world. On Puerto Rico’s roads, the distance you travel is measured in kilometres, while the speed you drive is in miles per hour. ‘Rai’ is typically used in Thailand to state land measures (one Rai is around 1 600 square metres). Go to the UK for a beer and you’ll likely get a pint.

Sometimes lingering older units can cause problems after metrification.

On 5 December 2003, twelve people were enjoying an adrenaline rush on the Space Mountain roller coaster at Tokyo Disneyland. Just before the end of the ride, it suddenly jolted and derailed, luckily without any injuries.

Excess vibration and stress had caused an axle to break. An investigation found that the axle was smaller than outlined in the design. The gap between the axle and bearing was designed to be 0.2 mm, but with this size error the gap was in fact over 1 mm.

The root cause? In 1995, the master plans of the ride were converted from Imperial to SI units. But when new axles were ordered in 2002, the old Imperial unit specifications design drawings were used by accident. Rather than 45 mm axels, 44.14 mm were ordered instead.

The ride re-opened three months later, much to the delight of all thrill-seekers taller than 40 inches… wait, I mean 102 cm.

Measurement miscommunication

In 2003, construction work began on a bridge over the river Rhine connecting Laufenberg, Germany and Laufenberg, Switzerland. The plan: engineers from each country would work on the bridge from their respective side of the river and meet in the middle.

The engineers were aware of a standardisation issue: sea level. In Germany, sea-level height is measured in relation to the North Sea. The Swiss team took their reference from the Mediterranean. Both sides knew they needed to account for a 270 mm difference in their reference points, so that’s what they did.

But an assessment during construction found a 540 mm discrepancy. It became apparent that when communicating the differences, the conversion was made with the wrong sign. The costly mistake meant the German side of the bridge needed to be lowered.

Ten years later, another major measurement mishap befell Europe. This time, it was France’s turn – more specifically, 1300 of the country’s train stations.

Looking to invest €15 billion in new trains, the nation’s state-owned train operator SNCF consulted the rail network operator that was then known as the RFF, requesting information on the country’s platform dimensions.

RFF provided measurements, but it turned out that the records on the width of France’s 8700 stations were incomplete, dating back only 30 years. Unfortunately, many regional platforms, built more than 50 years ago, were slimmer than the reported widths, and so the new trains wouldn’t be able to squeeze into the station.

The RFF quickly responded by ‘shaving’ down 300 older platforms at the cost of €50 million euros, but the damage was already done. Breaking the story, the satirical magazine Le Canard Enchaîné reported: “The Paris-Brest train is entering the station. Please pull in your stomachs.”

Share this blog to spread the message: never forget the importance of 100% quality!

Happy World Metrology Day!


  • Join our HxGN LIVE Events Worldwide

    Hexagon hosts exciting HxGN LIVE events around the globe! Experience our technology innovations in a location near you.

  • Recent Posts