What is the correct way to secure and adjust the harness on the Graco Slimfit 3-in-1?

Place your child with their back flat against the seat, bring harness straps over their shoulders, and buckle the crotch buckle. Connect the chest clip at armpit level, then pull the harness adjustment strap to tighten until snug—you should not be able to pinch excess webbing at the child's shoulder. The 10-position No-Rethread Simply Safe Adjust Harness System allows one-hand adjustment of the headrest and harness together.