The First Years introduces the True Fit SI(model C680). The SI stands for Side Impact, and the new contoured head rest is designed for better head control. The contoured design helps contain your child's head in the event of a crash. This seat features s a no rethread easy to adjust harness. The harness is for use from 5 to 35 pounds rear facing and up to 65 pounds in forward facing installations.Keeping your child rear facing longer is easy, the SI can be used rear facing up to 35 pounds. Did you ever try to rethread a harness on a car seat? Ours is hassle free,the harness adjusts simply by moving the side adjusters and they are clearly labeled to help with the correct positioning. The C680 model features smaller bottom rails and the patented Rebound Energy Management system, a flip up rebound bar that actually helps manage the rebound in the unlikely event of a crash, pull the bar forward and it snaps in place with your rear facing installation and flip it back when you move to the forward facing installation.This seat is fully lined with EPP foam and has deep side wings that really surround your child.The larger interior dimensions keep your child comfortable as they grow.We have added a center angle indicator in the front of our seat for use when installing in the rear facing position.This easy to read indicator will help you determine if you have installed your seat correctly.For your infant, it will assist in achieving the advocate recommended 45 degree angle for installation(without our head rest)and as you keep it rear facing to 35 pounds(with the head rest)you can check for the recommended 35 degree installation angle.We have LATCH attachments mounted on the sides so they are easy to access when you are installing your seat and easy to secure when you remove the seat from your vehicle. Installation is stress free with our color coded lock offs, whether you are installing for the first time rear facing or forward facing.