The world’s most perfect weight isn’t...  ...al cylinder known as the International Prototype Kilogram , or “Le Grand K.” Forged in 1879 from...  ...idium, it was hailed as the “perfect” kilogram —the gold standard by which other kilograms...

The International Prototype of the Kilogram in three nested bell jars (Photo: BIPM)...  ...art, you're not the only one - even the kilogram itself has put on weight: Using...  ...in the world -- the team have shown the original kilogram...