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World Metrology Day, Measurement Overkill, and Why Accuracy is the Wrong Word

2020-05-20  |  3 min read 

The History of World Metrology Day

May 20th is a day for the super nerds. I wasn’t even aware of its significance until less than a week ago.

145 years ago today seventeen nations signed The Metre Convention. At the time, in 1875, France owned both the official meter and the official kilogram – these are physical objects called “standards” – and the global community wanted a replacement and an organization to oversee maintenance of the standards. France was still recovering from rousing defeat in the Franco-Prussian War a few years prior and was keen to hand off the metric system to the international committee instead of the Germans, who had just given them a whooping.

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A few years later, in 1881, an attempt was made to define an electrical standard, starting with the Ohm, where resistance was defined using a 1 square mm column of mercury at 0 C that was 104.9 cm long, This was bumped to 106 cm long a year later in 1882, and again bumped to 106.3 cm in 1892. These were known as the BA ohm, the legal ohm, and the international ohm, respectively. And, both Kelvin and Tesla were actually in attendance at that last one. You’ve probably heard of them. The change from 106 to 106.3 came because they discovered standard they were using – wire coils – didn’t quite match the mercury spec so they had to tack on another 0.3 cm to make the equations balance.

The point I’m trying to make with all this, though, is that on May 20th a standard meter came to be, and from that we got the Ohm – which was based on the meter!

For world metrology day it just seemed fitting to bring in a couple folks who have known about this holiday a lot longer than me, and who work with modern standards all the time!

Watch the interview

Watch the whole EEs Talk Tech electrical engineering podcast interview here: