Petrie (in A Season in Egypt, 1887) states that his measurements were of the core masonry, and found the north and west sides to be 44°42 and 44°41' respectively, while he found the east and south sides to be 44°32' and 44°30' respectively.
He then states that the "mean" angle for the sides is 44°36' +/- 3', and follows this by saying that the "likely rule for its construction seems to be a slope of 7 on a base of 5, as this would require an angle of 44°34'40" ". (Petrie appears to have miscalculated from his tables here, however, as "a slope of 7 on a base of 5" actually reflects the slightly smaller angle of about 44°25'.)
Josef Dorner (in his Neue Messungen article of 1998) gives 44°44' for the average slope of the east side as taken from the "best preserved points on the finished surfaces" (my translation). He then went on to assume a slope of 45° for the structure as a whole.
The Red Pyramid indeed presents a complicated and intriguing story. I have wondered whether the apparently closely related differences in slope of the core masonry between the two sets of sides (i.e., the north and west vs south and east) might have been intentional for some reason. If so, then one assumes there must have been some correctional fudging done as construction proceeded in order to bring the four sides back in sync. If the difference found by Petrie between the two sets of sides is both real and intentional, then the obvious question is why would the building's designers have gone to the trouble to do this? Fertile ground for speculation here.
Might anyone know whether Stadelmann and Poltz have undertaken to resurvey the existing location of the entrance relative to the pyramid's original north base edge?
Lee Cooper