Why is it so easy to underestimate systematic errors when measuring G?

Before this Theo Murphy Meeting, my working hypothesis was that human activity during the measurement of G significantly affects the measurement itself. Noise caused by the gravity gradient of humans was indeed the reason why in one experiment the apparatus was raised 3 m above the floor. The meeting convinced me that all experimenters took adequate precautions against gravity gradients caused by human activity. During the meeting, another concern arose: was the cycle time between two states of the experiment so long that the environment changed significantly in the meantime? Once again, it appears that the experimenters were appropriately cautious. After the meeting, it became clear that ageing effects in thin, stressed wires could be an issue. I conclude with a speculation about a future 'atomic' value of G.