Jon wrote: Petrie says of obtaining an angle from the remaining casing stones at the North Face: "The angle by means of the large steel square was vitiated by the concretion on the faces of the stones being thicker below than above, .1 inch of difference making an error of 6'. The small goniometer was applied to the clear patches of the stone, selected in nine different parts. These three casing stones in situ have not as much weight assigned to them as they would otherwise have, owing to their irregularities.

and what do you think of the angles by theodolite?