The null balance method is used for precision force measurement in the precision industry in order to overcome the limitations of the load cell. The performance of any micro-weighing device is determined by the design of the precision mechanism. Such a device should be designed for high reproducibility, large measurement range with high resolution and fast response characteristics. The device consists of a displacement amplification mechanism and a parallel spring. The mechanism proposed here is analysed against the design specifications. The mechanism was designed for a resolution of 0.1 mg, a range of over 100 gf and a settling time of less than 1 s. The results of this design were verified by simulation and by experiment.