Wu et al. said:
Because our laboratory is about 4.5 km east of the San Francisco Bay, the ocean tidal loading effect on gravity at our location is significant and is not accurately described in available models (31). Figure 2B shows that the residual gravity variation is correlated to the water-level variation measured in the Bay. As shown in Fig. 2C and 2D, the ocean tidal loading leads to the peaks in the Allan deviation and the power spectral density in a period-band between 6-24 hours....
....Because the local gravity is affected by the tidal effects, the inaccurate tide model at our location constrains the accuracy of the long-term stability measurement and the systematic effect evaluation. A gravity comparison at a geophysical observatory would allow us to characterize them more accurately (34). With these improvements, a more accurate measurement of the ocean tidal loading effect may be useful....