def copy(from)
      @scalar      = from.scalar
      @numerator   = from.numerator
      @denominator = from.denominator
      @base = from.base?
      @signature   = from.signature
      @base_scalar = from.base_scalar
      @unit_name = begin
                     from.unit_name
                   rescue
                     nil
                   end
      self
    end
def copy(from)
      @scalar      = from.scalar
      @numerator   = from.numerator
      @denominator = from.denominator
      @base = from.base?
      @signature   = from.signature
      @base_scalar = from.base_scalar
      @unit_name = begin
                     from.unit_name
                   rescue
                     nil
                   end
      self
    end
Used to copy one unit to another
 @param [Unit] from Unit to copy definition from
 @return [Unit]