I believe that Josef Dorner has published the most recent (and most complete) survey data for the Red Pyramid - although there would appear to be curious lapses in how he then proceeded in using this data in his resulting computations.

See: Dorner, J. 1998. "Neue Messungen an der Roten Pyramide" in Heike Guks (ed.), Stationen: Beiträge zur Kultur- geschichte Ägyptens. R. Stadelmann gewidmet.

Dorner found an average slope angle of 44*44' (p. 25), and gave very precise figures for the base-length of each side (p. 24).

Bear in mind that these early pyramids were likely designed to simultaneously embody a variety of different relationships, and so a measurement taken at, or of, any particular point may carry a stronger reflection of but one of these factors, while a similar measurement taken elsewhere on the pyramid may have a stronger relevance to another of the originally chosen design factors.

Lee Cooper