5.22 An important part of the assessment at this point is the impact that the use of different financial structures have on the flexibility of the project to accommodate changes to the project requirements. In pursuit of least-cost contracts and certainty of affordability (i.e. unitary payments that are fixed except for the impact of inflation), procuring authorities have previously often used evaluation criteria which favour the maximum use of debt finance (the cheaper and relatively inflexible form of finance) and almost exclusively fixed interest rate debt, that further limits the flexibility to accommodate changes.