module Magick::RVG::Transformable

def scale(sx, sy = nil)

by sy. If sy is omitted it defaults to sx.
Multiply the x-coordinates by sx and the y-coordinates 
def scale(sx, sy = nil)
  sy ||= sx
  begin
    @transforms << [:scale, [Float(sx), Float(sy)]]
  rescue ArgumentError
    raise ArgumentError, "arguments must be convertable to float (got #{sx.class}, #{sy.class})"
  end
  yield(self) if block_given?
  self
end