*Radian* | *documentation* SI PlaneAngleMeasure. Symbol: rad. It is the angle of a circle subtended by an arc *equal* in length to the circle's radius. Another definition is: the plane angle *between* two radii of a circle which cut off on the circumference an arc *equal* in length to the radius. *Radian* = m/m = 1 | |

**has axiom** (*equal* (*MeasureFn* ?NUMBER *AngularDegree*) (*MeasureFn* (*MultiplicationFn* ?NUMBER (*DivisionFn* Pi 180)) *Radian*))
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**is an ***instance* of PlaneAngleMeasure | |

**is an ***instance* of SystemeInternationalUnit | |

PlaneAngleMeasure | **is first ***domain* of *CosineFn* | |

**is first ***domain* of *SineFn* | |

**is first ***domain* of *TangentFn* | |

ConstantQuantity | **is second ***domain* of *measure* | |

UnitOfMeasure | **is second ***domain* of *MeasureFn* | |

PhysicalQuantity | **is partitioned into** ConstantQuantity, FunctionQuantity | |

Abstract | **is ***disjoint* from Physical | |