What are the weight and height requirements for booster seat mode?

The booster seat weight requirement is 18 - 54.4 kg (40 - 120 lbs), the height requirement is 112 - 145 cm (44 - 57 in.) with the tops of the child's ears at or below the top of the booster seat headrest in high-back mode or the vehicle seat headrest in backless mode, and the child must be at least 4 years old. Once your child exceeds any of these size requirements, you must discontinue use of this seat. (Pages 5, 55, 59)