Hello Chris

The point I was making is they must have been using a predetermined angle because line of sight would not be possible.

I can see they might have the ability to measure and record a star angle but that does mean they used line of sight when constructing the GP shafts only that they were using a predetermined angle.

The predetermined angle is up for interpretation and it could be to point at stars but then maybe not. It’s the line of sight when constructing the shafts idea that is creating the problem.

CT > Its possible that as they approached the last 10 - 15m, they temporarily left out some blocks to enable the masons to check the angle of the shaft with a final sighting to the relevant star / asterism.

But does that not go back to the idea that each level was put down one at a time?

How did they go back and fill in a level and what is keeping the stones above the (temporary left out) stone from sliding down to the missing space?

RLH