Why rad += (k/180)*Math.PI on the snow tut?

"

onClipEvent (load) {

//variables

width = 300;

height = 200;

//random x,y, and alpha

this._xscale = this._yscale=50+Math.random()*100;
this._alpha = 20+Math.random() 50;
//random x and y for flakes
this._x = -width+Math.random()(3*width);

this._y = -10+Math.random()*height;

//speed and trigonometric value

i = 1+Math.random()*2;

k = -Math.PI+Math.random()*Math.PI;

rad = 0;

}

onClipEvent (enterFrame) {

// horizontal movement

rad += (k/180)*Math.PI;

"

It took me forever to realize that k is PI^2 without the math.random(), but now I do not understand why k/180*Math.PI again!

Why 180?

PI^2/180 then why * PI again?

Could someone tell me what each partâ€™s roles are?