Using a car seat is important enough, but what good is it if it isn't installed the right way? It applies regardless of whether the car seat is installed with the vehicle's seat belt or the lower anchor system, and it goes for both forward-facing car seats and safer rear-facing car seats, as well. The rule works like this: After installing the car seat, the seat or its base shouldn't move side-to-side or front-to-back more than 1 inch. First, read both the car seat instruction manual and the vehicle owner's manual. After that, position the car seat in the back seat and route the belt or lower anchor straps through.