On Dec. 10, 2014, the MIT Technology Review ran a story titled, “How to Measure Planck’s Constant Using Lego,” based on a paper by NIST researchers posted to Cornell University’s arXiv.org site. (“A LEGO Watt Balance: An Apparatus to Demonstrate the Definition of Mass Based on the New SI.” Click on PDF on the right-hand column of that page to download the entire paper.)

A watt balance compares the force on a mass due to gravity—its weight—with the force generated by an electric current in a magnetic field that just balances the weight. The NIST watt balance experiment is part of an international effort to develop a new definition for the kilogram based on fundamental natural constants. But looked at in a different way, it’s a method for determining Planck’s Constant—one of those fundamental values.

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