When you start with programming and you want to direct an object, then you'll need to know what number represents the direction you want. You'll also need to know this when you animate your sprites. If you know how angling and directioning works, then you'll also know that you always need to make your animation go counter-clockwise. You will be totally lost if you don't know anything about it, thus this article.

I have tried to make it simple, by this picture:
<img src="http://gmtutorials.com/files/angleex.PNG">

Simplier it can't be. But it is a common mistake. Hope everyone get it, and remember, "counter-clockwise ... always counter-clockwise".