How do I install the Diono Radian 3RXT Safe+ rear-facing?

Place the car seat rear-facing in the vehicle back seat. Ensure harness straps are at or just below your child's shoulders, and that top of head must be 1.5 inches below the car seat shell. Use either LATCH/UAS attachment (for children up to 35 lbs) or a combination with the adjustable bottom lowered for larger children. Always use anti-rebound bar when rear-facing. Tighten straps securely by grabbing sides and moving side-to-side and front-to-back until no more than one-inch of movement is possible. (Page 24-26)