In the spring of 1993, a major new 500 kV transmission line was put in service in Northern California. Test engineers initiated a series of artificial short-circuit faults to test the line installation. As an experiment, the steady-state and transient responses of the power system were recorded. During testing of the new California-Oregon Transmission Project (COTP), a PMU was installed at Olinda Substation near Redding, CA, and at Tracy Substation, near San Francisco, CA roughly 320 kilometers apart. PMU (phasor measurement unit) is a new measuring unit that recorded power system voltages and currents at the two substations. The PMUs use a navigational satellite system to synchronize digital sampling at different substations. That summer the data was analysed using modem digital signal processing software. In this article the author compares actual field measurements of the steady-state pre-fault power system angle with a classic relation for calculating real power flow on a transmission line. The agreement between the state-of-the-art measurements and the classic calculations was very close. >