This part of ISO/IEC 14143 defines the fundamental concepts of Functional Size Measurement (FSM) and describes the general principles for applying an FSM Method. This part of ISO/IEC 14143 does NOT provide detailed rules on how to: - measure Functional Size of software using a particular method, - use the results obtained from a particular method, or - select a particular method. NOTE - Guidelines on the uses of FSM are in Annex A. This part of ISO/IEC 14143 is applicable when determining if a method for sizing software is an FSM Method. It does not prevent the development of various methods, but rather provides a basis for assessing whether a particular method conforms to FSM. This part of ISO/IEC 14143 is intended for use by those persons associated with the acquisition, development, use, support, maintenance and audit of software.