The "pyramid diagonals" are among the most accurate of all the alignments linked with the Great Pyramid. The diagonals of the Great Pyramid are lines traced between the exterior corners of four "sockets" that encircle the pyramid. Each of these lines divides the surface of the pyramid into two identical and equally sized parts. The measurements along these lines provide very accurate estimates of phi (phi), the mathematical constant equal to 1.61803398.... This is one of several numbers that cannot be expressed as a simple fraction (fractional ratio) of integers (whole numbers). The Great Pyramid's diagonal measures approximately 220 feet (67 m). Because the apex stands at height 493.49 feet (149 m), this means that the base of the pyramid is about 8,100 square feet (750 sq m). This is more than enough space for two rooms with a combined area of more than 8,000 square feet (740 sq m). But the pyramid was not built as a house for Pharaoh Khufu; it is almost three times as large as the largest known Egyptian temple. The purpose of the pyramid is much more mysterious: It could be a place to worship God or contain pharaoh's body after death. Some scholars have suggested that the pyramid may have been used as a giant antenna during ancient Egypt's period of technological advancement when it was a center of astronomy.