What recline angle should I use for rear-facing, and how do I check it?

For rear-facing installation, lift up on the Recline Adjuster and tilt the seat so the Recline Ball on the Level Indicator is completely within the correct zone: White Zone for children weighing 1.8–9 kg (4–20 lbs), and Black Zone for children weighing 9–22.6 kg (20–50 lbs). The vehicle must be on level ground when checking the recline angle. Failure to properly recline the car seat could increase the child's risk of serious injury or death, as infants may have difficulty breathing in an upright position. (Page 62)