While we are waiting, and that may be for some time, let’s move on to the next part of the argument.
See below for part of the Great Indian Survey, this part performed about 1834, therefore well before GPS. The method was as follows. Establish two ‘baselines’, one at Dehra Doon (now Dehradun), the other at Sironj. The baseline is measured using the chain type tape measure, but with sophisticated and then state of the art compensation for thermal expansion. Drive a pillar into the ground, mark an arrow on it, then roll out the chain to full length and construct a second pillar, with an arrow marking the end point of the chain. There was all sorts of stuff they did to ensure the measurement was accurate.
Once the baseline is established between points A and B, find a third point C, measure the two angles BAC and ABC using a theodolite. From this it follows from Euclidean geometry (which is the geometry of a flat plane) that we can calculate the distances AC and BC.
Perhaps FE supporters might disagree with Euclid at this point, but that doesn’t matter. It least we know
where they disagree.
Knowing all three distances we can then find a fourth point, find the two relevant angles, then work out two new distances and so on. The point is to avoid the laborious tape measure method and extensive labour.
You note from the picture that they worked their way down from Dehradun to Sironj by this method, distance about 500 miles. Two of the final triangulation points were the
Sironj baseline, so they could compare the tape measure method with the triangulation method, including any accumulated errors. Supposedly the error was 7 inches in 500 miles, or 0.011%. That’s not bad, in my view.
Furthermore you can see they had another three sets of triangulation systems. In this way, over about 60 years, they covered the whole of India.
We still haven’t mentioned latitude and longitude (Hexagon please take note), nor the shape of the earth. Nothing but painstaking tape measure and angular measurement, with unbelievable accuracy for the time, in my view.