Calculations in the Newman–Penrose (NP) formalism of general relativity normally begin with the construction of a complex null tetrad , where is a pair of real null vectors and is a pair of complex null vectors. These tetrad vectors respect the following normalization and metric conditions assuming the spacetime signature * * * * In the context below, it will be shown how these three methods work. Note: In addition to the convention employed in this article, the other one in use is .