This video will show the installation of a Britax convertible rear-facing using the lower anchors (LATCH) and the rear-facing tether.
The Britax convertibles that this video applies for are the:
– Britax Marathon, Marathon Classic, Boulevard, Advocate, and Wizard
The new Britax convertibles (the Roundabout 55, Marathon 70, Boulevard 70, Advocate 70) are very similar in their installation – except I find that it is easier to get a tight installation if you pull the tails of the LATCH belts from inside the car seat, not outside. Please see this blog post for pictures of what inside vs outside means.
[youtube http://www.youtube.com/watch?v=E8fC5lsy2vU?rel=0]