Jon,
I thank you for the Stadellman and Fakhry information.
If one looks at the Dorner survey - where he measures an average casing-stone slope of 44°44', but then computes the elevation of the entrance assuming a slope of 45° - one finds that there is then (what I consider to be) a significant difference of about 1 foot in the determination of the entrance elevation. I see this as being significant because I believe it then calls into question whether the center of the pyramid's second chamber does indeed lie on the central vertical axis of the pyramid - as both the Perring and Dorner surveys have claimed to have found.
My proposed derivation analysis for the interior layout design of the Red Pyramid leads me to believe it possible that. in fact, the center of the second chamber lies about 3.3 to 4 feet north of the pyramid's central vertical axis. It is for this reason that I would be greatly interested to see the results of a meticulous modern survey (perhaps using laser technology?) that would once and for all determine the existing entrance passage location parameters relative to the pyramid's orginal north base edge, and following this, then determine the chamber locations relative to the north base edge.
Be that as it may, I do not know how Stadellman has arrived at his findings, but I do feel that there is wise caution both to surveyor and to the readers of surveys in Petrie's warning that the observor not modify an observation that is extremely near to being a theoretical angle so that it is then gven as being said theoretical angle (p.163 P&T).
It may simply be that there can never be an exacting and definitive answer to the question of the pyramid's overall as-built slope, only answers which give the apparent slope of certain specific limited sections of each side.
Lee Cooper