Effect of Local Magnetic Field in G Measurement with Time-of-Swing Method

The effect of the local time-varying magnetic field in our G measurement with the time-of-swing method is studied by magnifying the magnetic field to cause a perceptible change in the pendulum's period. The experimental result shows that the coefficients of the change in the period to the magnetic field are 37(1) and 12(1) ms/gauss in the two horizontal directions respectively, which means that the systematic uncertainty due to the local magnetic field is less than 0.4 ppm in our G measurement.