Geographical mile longitude at the equator is thus exactly 60 geographical miles. It was closely related to the nautical mile, which was originally determined as 1 minute of arc along a great circle of the Earth, but is nowadays defined as exactly 1852 metres. The US National Institute of Standards and Technology (NIST) notes that: "The international nautical mile of 1 852 meters (6 076.115 49...feet) was adopted effective July 1, 1954, for use in the United States. The value formerly used in the United States was 6 080.20 feet = 1 nautical (geographical or sea) mile." (6080.2 feet is 1853.24496 meters.)
Phasor measurement unit Phasor measurement unit A phasor measurement unit (PMU) is a device used to estimate the magnitude and phase angle of an electrical Phasor quantity like voltage or current in the electricity grid using a common time source for synchronization. Time synchronization is usually provided by GPS and allows synchronized real-time measurements of multiple remote measurement points on the grid. PMUs are capable of capturing samples from a waveform in quick succession and reconstruct the Phasor quantity. The resulting measurement is known as a synchrophasor. These devices can also be used to measure the frequency in the power grid. A typical