Before reading this, I knew how the length of a metre was set but I did not know how the original kilogram was set. The members of the International Bureau of Weights and Measures are to vote on Friday whether to set the weight of a kilogram to be defined by the Planck constant. The method of setting the weight of a kilogram needs to be looked at as the piece of platinum-iridium, despite being kept carefully does not always weigh the same, as it still manages to attract dust and dirt even within 3 bell jars.
(The news story link that was here no longer works as the story has gone)
