This is 2 parts and a bit long but should show how it works:
https://www.youtube.com/watch?annotation_id=annotation_170809&feature=iv&src_vid=2bCjzLij54k&v=jDlkl78Yf-8
https://www.youtube.com/watch?annotation_id=annotation_25534&feature=iv&src_vid=jDlkl78Yf-8&v=2bCjzLij54k