As an example, for a quantum field theory with one massless scalar field and one self-coupling term, denote the bare field strength by ϕ ϕ 0 and the bare coupling constant by g 0 . In the process of renormalisation, a mass scale M must be chosen. Depending on M, the field strength is rescaled by a constant: ϕ ϕ = Z ϕ ϕ 0 , and as a result the bare coupling constant g 0 is correspondingly shifted to the renormalised coupling constant g.