What are the guidelines for using the Graco car seat in booster mode?

Booster mode can be used for children weighing 30-100 lbs (14-45 kg), with a height of 38-57 inches (96-145 cm), and at least 4 years old. The vehicle seat's lap belt must lay low on the child's hip and be routed behind the armrest in the booster's belt path (marked with a green label). The shoulder belt must be centered between the child's neck and edge of shoulder. Never use a vehicle lap-only seat belt in booster mode, and do not allow the child to slouch or slide down. (Page 27)