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Electromagnetic units (EMU). This system is based on Ampère’s law, which defines the unit of electric current once you select an appropriate value for the constant C. When dealing exclusively with magnetic effects, it is convenient to set C = 1. If CGS units are used for the remaining basic dimensions, the current unit is called an abampere, and the corresponding coherent unit system is called electromagnetic units. Unique names for derived units have been introduced by prefixing the SI name with ab-. For a list of EMU units, see Special EMU Units.
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Electrostatic units (ESU). Based on Coulomb’s law for the force between point charges, ESU uses a unit of charge called the statcoulomb with CGS units for length, mass, and time. From there, the statampere, or franklin, and other derived units of the electrostatic unit system follow. For a list of ESU units, see Special ESU Units.
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British engineering units. An alternative to the standard FPS system is the British engineering unit system (also called gravitational foot-pound-second system or foot-slug-second system). Here, the pound force is the natural unit of force, which causes the introduction of the mass unit slug such that a pound force is a slug-foot per second squared. For a list of British engineering units, see Special British Engineering Units.
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Inch-pound-second unit system (IPS units). It is possible to define varieties of the FPS and British engineering systems based on the inch instead of the foot as basic unit of length. This gives rise to two distinct inch-pound-second systems: the absolute IPS system (just called IPS) and the gravitational IPS system. For a list of IPS units, see Special IPS Units.
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