I figure out now about the Factors parameter. It's an array that stands for the minor unit for Y-Axis and represents how many subdivisions the scale can have, depending on the max and mix axis values.
Code:
$settings = array("Factors"=>array(1,2));
$pic->drawScale($settings);
The code above sets the minor unit for one or half, as 0---0.5---1---1.5---2---2.5---3.
Code:
$settings = array("Factors"=>array(1));
$pic->drawScale($settings);
The code above sets the minor unit for one , as 0---1---2---3...
I hope it helps!