# The way we define kilograms, meters and seconds changes today

phys.org | 12/31/1969 | Staff
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We measure stuff all the time—how long, how heavy, how hot, and so on—because we need to for things such as trade, health and knowledge. But making sure our measurements compare apples with apples has been a challenge: how to know if my kilogram weight or meter length is the same as yours.

Attempts have been made to define the units of measurement over the years. But today—International Metrology Day—sees the complete revision of those standards come into play.

#### Transition

You won't notice anything—you will not be heavier or lighter than yesterday—because the transition has been made to be seamless.

Just the definitions of the seven base units of the SI (Système International d'Unités, or the International System of Units) are now completely different from yesterday.

#### Humans - Lengths - Weights - Time

Humans have always been able to count, but as we evolved we quickly moved to measuring lengths, weights and time.

The Egyptian Pharaohs caused pyramids to be built based on the length of the royal forearm, known as the Royal Cubit. This was kept and promulgated by engineer priests who maintained the standard under pain of death.

#### Cubit - Unit - Time—it - Meter - Tens

But the cubit wasn't a fixed unit over time—it was about half a meter, plus or minus a few tens of millimeters by today's measure.

The first suggestion of a universal set of decimal measures was made by John Wilkins, in 1668, then Secretary of the Royal Society in London.

#### Impetus - Something - Revolution - Standards - Length

The impetus for doing something practical came with the French Revolution. It was the French who defined the first standards of length and mass, with two platinum standards representing the meter and the kilogram on June 22, 1799, in the Archives de la République in Paris.

Scientists backed the idea, the German mathematician Carl Friedrich Gauss being particularly keen. Representatives of 17 nations came together to create the International System of Units by signing the Metre Convention...