What are the weight and height requirements for using the car seat with the built-in harness?

Your child must weigh between 20 to 40 lbs (9 to 18 kg) and be between 27 to 43 inches (69 to 109 cm) in height. Your child must also be at least one year old, able to sit upright unassisted, and have shoulders below the top harness slots. If your child's shoulders are above the top harness slots, they are too large for the built-in harness. (Page 10)