The Written Scheme of Examination (WSE) is a document that details Safety Devices and components associated with a pressure system; it defines the system in operation, the safety devices present, as well as the type and frequency of thorough examinations required. The document also lays out periods for any additional inspections required for each device or component. Under the Pressure Systems Safety Regulations 2000 (PSSR), users and owners of most pressure plant must have a WSE.