This is a standard for synchronized phasor measurement systems in power systems. It addresses the definition of a synchronized phasor, time synchronization, application of timetags, method to verify measurement compliance with the standard, and message formats for communication with a phasor measurement unit (PMU). In this context, a PMU can be a stand-alone physical unit or a functional unit within another physical unit. This standard does not specify limits to measurement response time, accuracy under transient conditions, hardware, software, or a method for computing phasors. This standard defines synchronized phasor measurements in substations so that the measurement equipment can be readily interfaced with associated systems. It specifies data formats and synchronization requirements to allow correlating phasors from various sources and compares them with similar data from different measurement systems. Revision Standard - Superseded. This standard defines synchronized phasor measurements used in power system applications. It provides a method to quantify the measurement, tests to be sure the measurement conforms to the definition, and error limits for the test. It also defines a data communication protocol including message formats for communicating this data in a real-time system. Explanation, examples, and supporting information are also provided.