This part of IEC 61400 defines an information model from which time-based@ and productionbased availability indicators for services can be derived and reported. The purpose is to provide standardised metrics that can be used to create and organise methods for availability calculation and reporting according to the user??s needs. The document provides information categories@ which unambiguously describe how data is used to characterise and categorise the operation. The information model specifies category priority for discrimination between possible concurrent categories. Further@ the model defines entry and exit criteria to allocate fractions of time and production values to the proper information category. A full overview of all information categories@ exit and entry criteria is given in Annex A@ see Figure A.1. The document can be applied to any number of WTGSs@ whether represented by an individual turbine@ a fleet of wind turbines@ a wind power station or a portfolio of wind power stations. A wind power station is typically made up of all WTGSs@ functional services and balance of plant elements as seen from the point of common coupling. Examples are provided in informative annexes which provide guidelines for calculation of availability indicators: ? examples of optional information categories@ Annex B; ? examples of application of the information categories for determination of availability@ Annex C; ? examples of application scenarios@ Annex D; ? examples on methods for determination of potential production@ Annex E; ? examples of how to expand the model to balance of plant elements@ Annex F. This document does not prescribe how availability indicators shall be calculated. The standard does not specify the method of information acquisition@ how to estimate the production terms or to form the basis for power curve performance measurements ?C which is the objective of IEC 61400-12. A degree of uncertainty is inherent in both the measurement of a power curve and the calculation of potential energy production. The stakeholders should agree upon acceptable uncertainty parameters.