A kilogram equal to the mass of a rod, Standard, made of alloy, platinum-iridium, which inside a set awning a nesting that it from pollution and inappropriate use maintains and in the Bureau of international weights and measure in Sur, etc. outside of Paris. maintained.After a while, the scientists saw that the mass of this rod is reduced! For this reason, scientists are making butter from crystals that are bigger than, quite specifically, a kg.