It was Petrie's theory that the inner structure and the descending passage were the basis of the orientation, not the final finish of the casing sides, and he assumed that the alignment to the pole of the night sky was near to perfect so as then to deduce the change in the position of the pole since the third millennium BC supposing that the currents in the oceans were shifting the land.

On this basis, without the oceanic theory, there is a build error difference between the casing and the core which results in a closer alignment fortuitously so, and actually we have to go back to Smyth's determination of the azimuth of the the Entrance Passage and the east side of the corner sockets to get the the original alignment, which inevitably has some error, assuming we should prefer the determinations of a professor of observational astronomy over a young amateur surveyor and that plate tectonics have not changed the alignment of the Giza plateau to a significant extent.

Mark