section_path: Construction/Surveys and design
section_name: Surveys and design
paragraph_text: Surveys and design
  
  The first precise measurements of the pyramid were made by Egyptologist Flinders Petrie in 1880–1882, published as The Pyramids and Temples of Gizeh. Many of the casing-stones and inner chamber blocks of the Great Pyramid fit together with high precision, with joints, on average, only 0.5 millimetres (0.020 in) wide. On the contrary, core blocks were only roughly shaped, with rubble inserted between larger gaps. Mortar was used to bind the outer layers together and fill gaps and joints.
  
  The block height and weight tends to get progressively smaller towards the top. Petrie measured the lowest layer to be 148 centimetres (4.86 ft) high, whereas the layers towards the summit barely exceed 50 centimetres (1.6 ft).
  
  The accuracy of the pyramid's perimeter is such that the four sides of the base have an average error of only 58 millimetres (2.3 inches) in length and the finished base was squared to a mean corner error of only 12 seconds of arc.
  
  The completed design dimensions are measured to have originally been 280 royal cubits (146.7 m; 481.4 ft) high by 440 cubits (230.6 m; 756.4 ft) long at each of the four sides of its base. Ancient Egyptians used seked – how much run for one cubit of rise – to describe slopes. For the Great Pyramid a seked of 5 + 1 / 2 palms was chosen, a ratio of 14 up to 11 in.
  
  Some Egyptologists suggest this slope was chosen because the ratio of perimeter to height (1760/280 cubits) equals 2 π to an accuracy of better than 0.05 percent (corresponding to the well-known approximation of π as 22/7). Verner wrote, "We can conclude that although the ancient Egyptians could not precisely define the value of π, in practice they used it". Petrie concluded: "but these relations of areas and of circular ratio are so systematic that we should grant that they were in the builder's design". Others have argued that the ancient Egyptians had no concept of pi and would not have thought to encode it in their monuments and that the observed pyramid slope may be based on the seked choice alone.