How do I know if the harness height is adjusted correctly?

For rear-facing use, the harness straps should be at or just below the child's shoulders, with the top of the head at least 1 inch (2.5 cm) below the headrest adjustment lever (page 18). For forward-facing use, the harness straps should be at or just above the child's shoulders, with the top of the child's ears below the top of the headrest (page 18).