A determination of Planck's constant using the NRC watt balance

We have measured Planck's constant and have obtained a value of 6.626?070?34(12)???10?34?J?s. To our knowledge this measurement of h has the lowest uncertainty reported to date. This result has been obtained from measurements of four masses of different material and nominal values varying from 1?kg to 250?g. The experimental procedures and the measurement uncertainties are described in detail.