[CROSSBOLT]

I searched and found one topic about plumb bobs and discussion about a deep mine. But I propose a simpler approach. I am pasting a Wikipedia description only to guarantee we all understand the device and how it was used.

My question is to what does the plumb bob point?

https://en.m.wikipedia.org/wiki/Plumb_bob

[Everette Graham]

Plumb bobs point to Earth's center of mass because gravity acts as a vector field radiating toward that center. So basically, plum bobs point directly down. Do remember, though, that when I say down, I mean down as in the localized manifestation of Earth's gravitational field.