AbstractThis paper presents a demonstration of a methodology for fault removal during software development. The methodology encompasses the entire development history, from system and software requirements generation to system test. Thus it considers not only the faults during software testing after formal configuration controls have been invoked, but also the faults discovered prior to that phase: during system and software requirements generation, preliminary design, detailed design and code and unit testing.The agents for fault discovery used in verification and validation are called activities, techniques and tools (AT&Ts) in this paper, each having a certain maximum potential or capability for fault discovery. The AT&Ts considered include the usual specification review activities, and also certain tools not normally applied in ‘standard’ software development, such as automated requirements aids.Application of the methodology yields numbers of residual faults as of each phase of development, including those remaining to be discovered during operations and maintenance. Some previous experience and data on residual faults correspond to these results, indicating that the methodology and choice of parameters are reasonable.The methodology also allows one to calculate a relative loss due to delay in fault discovery, which, as is well known, rises rapidly when faults are not discovered during the phase in which they are genera