Watt Balance (IMAGE) American Institute of Physics Caption The NIST-4 watt balance is shown. The instrument recently took its first full measurements of Planck's constant, an important step toward redefining the kilogram. Credit Jennifer Lauren Lee/NIST PML Usage Restrictions With proper attribution License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.