By Margaret Beasley,
Rachel Stevens, and
Max Cacas
Reporter
Federal News Radio

Most people take for granted what a kilogram of flour is supposed to weigh. But who determines officially what that kilogram is supposed to be?

Two scientists at the National Institute of Standards and Technology in Gaithersburg, Maryland deal with that every day.

Patrick Abbott, a metrologist with the NIST’s mass and force group, maintains the United States’ kilogram mass standards.

While it might sound mundane, Abbott says the kilogram mass standard is extremely important for trade.

“To have just a small error in every ton of grain or every pharmaceutical drug that’s made and sold, a very small error very quickly adds up to a lot of money,” Abbott explains.

It’s not a new idea.

“To have a unit that everybody can agree on has been important from the beginning of time. If you think about it, even at a basic level, years ago, when people would trade one kind of grain for another kind of crop, in order to assure a fair trade, somebody had to have a scale that everyone believed in,” Abbott says.

And NIST takes the accuracy of its scales very seriously.

Each of the stainless steel, cylindrical objects is kept in a thermally-stable chamber behind glass. Even something as minute as a fingerprint could throw off their accuracy, Abbott says.

“Standard practice in the mass world is you cannot, must not, ever touch any of the weights with fingers.”

In a separate vault, NIST keeps its two copies of the international prototype kilogram, which are made of the same batch of platinum iridium as the original in Paris. Abbott says every nation that is a signatory to the Treaty of Meter Convention has at least one of these replicas.

And, if the physical international standard is not precise enough for you, you might be interested in the work of Abbott’s colleague, Dr. Richard Steiner.

Steiner is a research physicist at NIST, and one of only a handful of scientists in the world currently working on developing the electronic kilogram. The aim of the project is to avoid accuracy losses associated with using physical measures.

“The ultimate goal is to basically measure a kilogram standard in electronic terms, because the electronics are all dependent on fundamental constants,” Steiner explains.

Steiner says his work depends on equations created using precise, scientific measures of atomic time, laser length, voltage and resistance. In layman’s terms: “What we’re trying to do is make a kind of an electronic absolute calibrated bathroom scale,” Steiner says.

The goal may be within reach. Steiner says a recent conference in South Korea showed that scientists worldwide are beginning to find similar results in their work.

“As of five years ago, the numbers were spread out quite a bit. Now they seem to be converging.”

While the world is not quite ready to rely on the electronic kilogram just yet, Abbott says it is a worthy goal.

The physical international kilogram prototype in Paris has drifted in mass ever-so-slightly over the past 100 years, Abbott says. That means it’s not as accurate as it used to be. And that, Abbott says, “serves as a motivation for an electronic kilogram.”

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Margaret Beasley and Rachel Stevens are interns for Federal News Radio.

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