def conversion_factor
      use_dimension
      f = @factor
      @dim.each do |k,d|
        if d != 0
          u = LIST[k]
          if u.dimensionless?
            f *= u.dimension_value**d
          end
        end
      end
      f
    end
def conversion_factor
      use_dimension
      f = @factor
      @dim.each do |k,d|
        if d != 0
          u = LIST[k]
          if u.dimensionless?
            f *= u.dimension_value**d
          end
        end
      end
      f
    end
Conversion Factor to base unit, including dimension-value.
 @return [Numeric]
 @example
   Phys::Unit["deg"].dimension         #=> {"pi"=>1, "radian"=>1}
   Phys::Unit["deg"].factor            #=> (1/180)
   Phys::Unit["deg"].conversion_factor #=> 0.017453292519943295
 @see #factor