The most difficult en­gi­neer­ing riddles

The porous light stone was used in the concrete of the dome to reduce its weight. Scientists estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater. The same technique was for the ceilings of the Colosseum.

In engineering and science, one often has a number of data points, obtained by experimentation, which represent the values of a function for a limited number of values of the independent variable. It is often required to interpolate (i.e., estimate) the value of that function for an intermediate value of the independent variable.

The Kola Superdeep Borehole is the result of a scientific drilling project of the Soviet Union in the Pechengsky District, on the Kola Peninsula. The project attempted to drill as deep as possible into the Earth's crust. Drilling began on 24 May 1970. The deepest, SG-3, reached 12,262 metres (40,230 ft; 7.619 mi) in 1989 and is the deepest artificial point on Earth, as of April 2019. The borehole is 23 centimetres (9 in) in diameter.