last week, we had measured the magnetic field against water NMR frequency. However, the magnetic field calculated from the Hall probe has 10% different from theoretical value. we think that it may be due to the position of the hall probe is not on the crystal site but lower, about 50mm. and the separation of the Helmholtz coil is 150mm.

thus, we take out the crystal, and replace it with another hall probe. we found that the magnetic field was much closer to the theoretical value. Although it is closer, and the different is 0.0038 Tesla to the theoretical value. which is 1% to 2% error. Thus, we think this error is due to the horizontal position.