Quetta and Ronna listed as new prefixes for SI measurement


It can now be said that the Earth weighs about six ronnograms instead of 6,000 yottagrams. Jupiter can be described as having a mass of about 1.9 quettagrams, rather than just 1.9 million yottagrams. And the weight of an electron is one rontogram, or 0.001 yoctogram.

The opportunity to more succinctly describe the weight of our planet and the particles of our visible world comes after a meeting of scientists and officials in the Paris suburbs that ended Friday. Participants at the 27th Session of the General Conference on Weights and Measures agreed to introduce the ronna, quetta, ronto, and quecto as prefixes for the International System of Units, more commonly known as the metric system.

It was the first time since 1991 that scientists approved the expansion of prefixes in the global measurement system.

Ronna refers to using 27 zeros after a first digit – or 1,000,000,000,000,000,000,000,000,000 – and quetta means there are 30 zeroes. Ronto is the reverse of Ronna, making it 0.00000000000000000000000001, while quecto is the inverse of quetta. The newest members of this prefix club join the more familiar kilo (1,000), mega (1,000,000), milli (0.001), and micro (0.000001).

“At first glance, this may not sound like a particularly exciting change,” Oliver Jones, a professor of environmental chemistry at Australia’s RMIT University, wrote in an email. But “standard prefixes, which are the same all over the world, help us say what we mean and for others to understand us.”

The latest additions were “driven by the growing demands of data science and digital storage, which already use prefixes at the top of the existing range,” Britain’s National Physical Laboratory said in a statement. All of the world’s data will be about 175 zettabytes (21 zeroes) or about 0.175 yottabytes by 2025, predicts market research firm IDC.

Scientists are about to change what a kilogram is. That’s huge.

Richard Brown, NPL’s head of metrology or measurement, presented the four new prefixes for approval by delegates representing the 64 countries, including the United States, that are members of the International Bureau of Weights and Measures.

The new terms are needed as the amount of digital data grows, Brown told the Associated Press. “Over the past 30 years, the datasphere has grown exponentially and data scientists have realized that they will run out of words to describe the levels of storage,” he said.

Jones, the RMIT professor, said the new units “help us manage digital infrastructure, make scientific progress and sustain society, which is why this change is important.”

Ronna, ronto, quetta and quecto were selected because the letters R and Q are not used for existing prefixes, Brown added. The symbols for ronna and quetta are R and Q respectively, while those for ronto and quecto are r and q.

Regular use of the most recent additions to the measurement system is likely limited to scientists and data professionals. But the conference participants said the prefixes should be introduced preemptively to prevent unofficial prefixes from being adopted.

The delegates also agreed to stop adding leap seconds to official clocks by 2035. These had been used to compensate for the difference between atomic time and the Earth’s slowing rotation. Leap seconds can create “discontinuities that can cause serious disruptions to critical digital infrastructure,” including those that dictate global telecommunications and energy transmission systems, the conference said.

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