The seat belt is the preferred method of installation for the Revolve360™ Extend because it allows you to take advantage of a true one-time installation. The tether must be used in both rear-facing and forward-facing harness installations, regardless of whether you have the car seat base installed with the seat belt or lower anchors (LATCH/UAS). IMPORTANT: When installing with the vehicle seat belt, your vehicle seat belt MUST be locked to ensure accurate and safe installation.