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Most rear-facing seats consist of two parts: the base and the infant carrier. You will install the base, the part that remains in the car. Follow the manufacturer's instructions for removing the carrier from the base. Usually, there is simply a lever or button to activate. Many car seat bases include an attached belt with two hooks that can latch onto designated spots near your car's seat belt area. If your car manufacturer included these, snap the hooks onto the metal bars at those designated spots. Tighten the anchor belt attached to the base until the base is snug against the seat. Check the manufacturer's instructions if you aren't sure if your car or seat has this option, or how to use it. There may also be a place to feed the car's seat belt through the base for added security. If your car seat does not use the anchor system, it will be secured to the backseat with the car's seat belt. Feed the belt through designated openings in the base and buckle it. The seatbelt should fit cleanly, and not be twisted or bunched up. Read the instructions to study where you are supposed to put the belt if you aren't sure. Every vehicle and seat is different, so it's important to get this right. Not latching the seat belt correctly can increase the risk of the child getting injured in an accident. Set it onto the base so that the child would face the rear. It should click when it's in the right position. You can then practice taking the carrier out (by activating the lever or button) and setting it back into get a feel for things. Rear facing car seats usually have bases that can rest at different angles. The youngest infants will need to be in the more reclined position. This helps them breathe properly. Most infant carriers have level indicators. Once yours is in place, read this level to see if the seat is at the correct angle for the babies weight/height/age. Check the manufacturer's instructions for how to properly read the level if it isn't clear. Change the base angle if the level is not correct or your child. Usually, this involves turning the base over and rotating a piece. Remember to change the angle later on (or switch to a different seat) if the baby outgrows one setting.
Separate the carrier from the base. Anchor the base to your car's back seat. Thread the seat belt through the base, alternatively. Pop the infant carrier into the base. Double check the base angle.