The legal process to change the definition of the kilogram is already underway, but it had been decided that no final decision would be made before the next meeting of the General Conference on Weights and Measures in 2011. (For more detailed information, see kilogram definitions.) The Planck constant is a leading contender to form the basis of the new definition, although not the only one. Possible new definitions include "the mass of a body at rest whose equivalent energy equals the energy of photons whose frequencies sum to 7050135639273999999♠135639274×1042 Hz", or simply "the kilogram is defined so that the Planck constant equals 6966662606895999999♠6.62606896×10−34 J⋅s".
Was the Planck constant the only option for redefining the kilogram?
The Planck constant is a leading contender to form the basis of the new definition, although not the only one