public function lineScale($x1, $y1, $x2, $y2)
{
$x1 = ($x1 - $this->_xMin) / $this->scale + $this->leftMargin;
$y1 = ($y1 - $this->_yMin) / $this->scale + $this->topMargin;
$x2 = ($x2 - $this->_xMin) / $this->scale + $this->leftMargin;
$y2 = ($y2 - $this->_yMin) / $this->scale + $this->topMargin;
$this->Line($x1, $y1, $x2, $y2);
}