def **(other)
      if other.is_a?(Numeric)
        new(value ** other, unit ** other)
      else
        fail TypeError, "Can't raise #{self} to #{other} power."
      end
    end
def **(other)
      if other.is_a?(Numeric)
        new(value ** other, unit ** other)
      else
        fail TypeError, "Can't raise #{self} to #{other} power."
      end
    end
Raise a measurement to a numeric power.
 @param number [Numeric]
 @example
   measurement ** 2
 @api public