How does the automatic line advancement work, and what do I do if it stops feeding?

This trimmer is equipped with automatic line advancement, which automatically feeds additional line to the correct length as it wears down during use. If the line does not auto advance, the trimmer line may be tangled or empty — stop and restart the trimmer, which will automatically advance the line 1/4 inch (6.4 mm) upon starting. (Page 14)