Wikipedia
The seked (or seqed) was an ancient Egyptian unit of measure for the inclination of the triangular faces of a right pyramid. The system was based on the Egyptian's length measure known as the royal cubit. The royal cubit was subdivided into seven palms and each palm was further divided into four digits. The inclination of measured slopes was therefore expressed as the number of palms and digits moved horizontally for each royal cubit rise.
Information on the use of the seked in the design of pyramids has been obtained from two mathematical papyri; the Rhind Mathematical Papyrus in the British Museum and the Moscow Mathematical Papyrus in the Museum of Fine Arts. Although there is no direct evidence of its application from the archaeology of the Old Kingdom, there are a number of examples from the two mathematical papyrii, which date to the Middle Kingdom that show the use of this system for defining the slopes of the sides of pyramids, based on their height and base dimensions. The most widely quoted example is perhaps problem 56 from the Rhind Mathematical Papyrus.
The most famous of all the pyramids of Egypt is the Great Pyramid of Giza built around 2,550 B.C.. Based on the surveys of this structure that have been carried out by Flinders Petrie and others, the slopes of the faces of this monument were a seked of 5 1/2, or 5 palms and 2 digits [see figure above] which equates to a slope of 51.84° from the horizontal, using the modern 360 degree system. This slope would probably have been accurately applied during construction by way of 'A frame' shaped wooden tools with plumb bobs, marked to the correct incline, so that slopes could be measured out and checked efficiently.
Furthermore, according to Flinders Petrie's survey data in "The Pyramids and Temples of Gizeh" the mean slope of the Great Pyramid's entrance passage is 26° 31' 23" ± 5". This is less than 1/20th of one degree in deviation from an ideal slope of 1 in 2, which is 26° 33' 54".
This equates to a seked of 14, and is generally considered to have been the intentional designed slope applied by the Old Kingdom builders for internal passages.