What is the proper angle and recline position for rear-facing installation?

The car seat must be adjusted to one of the three rear-facing recline positions so that the level line is parallel to the ground. Infants may have difficulty breathing when in an upright seated position, so make sure they recline enough for their head to lie back comfortably and safely. In some vehicles, you may need to place a tightly rolled towel or small blanket beneath the front edge of the car seat to provide enough recline so that the level line is parallel to the ground. (Pages 28, 34)