| UnitOfMeasure |  | A standard of measurement for some dimension.  For example, the Meter is a UnitOfMeasure for the dimension of length,  as is the Inch.  There is no intrisic property of a UnitOfMeasure that  makes it primitive or fundamental; rather, a system-of-units (e.g.  SystemeInternationalUnit) defines a set of orthogonal dimensions and  assigns units for each | PhysicalQuantity | SubtractionFn | MeasureFn | (=>(and
 (instance ?REL RelationExtendedToQuantities)
 (instance ?REL BinaryRelation)
 (instance ?NUMBER1 RealNumber)
 (instance ?NUMBER2 RealNumber)
 (holds ?REL ?NUMBER1 ?NUMBER2))
 (forall (?UNIT)
 (=>
 (instance ?UNIT UnitOfMeasure)
 (holds ?REL (MeasureFn ?NUMBER1 ?UNIT) (MeasureFn ?NUMBER2 ?UNIT)))))
 
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