The Pyramids and Temples of Gizeh by Sir Flinders Petrie -
Outside of Great Pyramid  The Pyramids and Temples of Gizeh by
W. M. Flinders Petrie  Chap. 6. Outside of Great Pyramid Pages
37 - 54  20 p. 37 The materials available for a discussion of
the original size of the base of the Great pyramid are :  (1)
the casing in situ upon the pavement, in the middle of each
face; (2) the rock cut sockets at each corner; (3) the levels of
the pavement and sockets; (4) the mean planes of the present
core masonary.  Since the time of the first discovery of some of
the sockets in 1801, it has always been supposed that they
defined the original extent of the Pyramid, and various
observers have measured from corner to corner of them, and
thereby obtained a dimension which waswithout further inquiryput
down as the length of the base of the Pyramid. But, in as much
as the sockets are on different levels, it was assumed that the
faces of the stones placed in them rose up vertically from the
edge of the bottom, until they reac