No Weigh

Somewhere in Paris, carefully guarded, sits a platinum and iridium cylinder, about the size of a golf ball, called the Grand Kilogram. Scientists made it more than 100 years ago to define the kilogram or kilogramme. All other kilogram weights are measured against it (in a sense). It's our basic unit of mass.

But what does the Grand Kilogam weigh? Let’s suppose that it weighs exactly what the Grand Kilogram weighs. If you compare it to itself, it will weigh, redundantly, exactly one kilogram. That will tell you little.

You can weigh the Grand Kilogram against copies of itself (and scientists do this). The weights will differ. 

The problem is that the Grand Kilogram has lost mass over the last 100 years, perhaps because of decaying impurities in the metal. No one is certain. According to the Corporate Democrat, the loss is “about the weight of an eyelash.” As a consequence, most kilogram measurements around the world have become different in a way that can sometimes have an impact on science and technology. But I got lost somewhere—tell me again how we determine what the Grand Kilogram weighs? 

(With thanks to Ludwig Wittgenstein)