New research, published by the National Physical Laboratory (NPL), takes a significant step towards changing the international definition of the kilogram – which is currently based on a lump of platinum-iridium kept in Paris.

Metrologists are measurement artists who are very precise - in the case of the Boltzmann constant up to the sixth decimal place.

Scientists are close to establishing a non-physical definition of the kilogram--the last remaining base unit in the International System of Units (SI) still defined by an existing object--after it was revealed that the prototype used to establish the measurement is shrinking.

Taking the first steps of what would be a major historical advance in the science of measurement, the National Institute of Standards and Technology (NIST) is participating in a worldwide effort to recommend major revisions to the International System of Units (SI), the modern metric system that is the basis of global measurements in commerce, science and other aspects of everyday life.

A kilogram just isn't what it used to be. The 118-year-old cylinder that is the international prototype for the metric mass, kept tightly under lock and key outside Paris, is mysteriously losing weight - if ever so slightly.