The US National Institute of Standards and Technology (NIST) has recently revised its value for Planck's constant — a number it uses to define a kilogram — and had come up with a more precise definition. Max Planck, from whom the constant is derives, was a pioneer of quantum physics, and worked on, amongst other things, the quantisation of energy, which lies at the heart of quantum theory. He worked out that heat radiation is given off by vibrating atoms, and the frequencies of the radiated waves were all multiples of a base figure he called h — Planck's constant — and can be multiplied by the frequency of a wave to determine its overall energy. Einstein showed the there is a relationship between energy and mass, and so Planck's constant can also be used to describe the mass of an object. The scientists determined that the new definition for a kilogram has an uncertainty of just 13 parts per billion, beating NIST's last measurement, which had an uncertainty of 34 parts per billion. To find out more go to New Measurement Will Help Redefine International Unit of Mass.