I skipped a week, (or two) oh well who's counting. Back in my first post a friend asked a very good question. So, I thought I would just answer that for this post.
"This might sound dumb but why can't you use the latch system and the seat belt?? We thought that would be extra safe. I would love to know if I should only use one."
Not a dumb question at all. You should absolutely only use one. There is no need for both. In general, you use whichever system results in a more secure installation for the seat in your car. That is the one that is safer.
Car seats are designed to handle crash forces in specific ways. While we know, thanks to crash testing, that baby's car seat will withstand crash forces when installed with the seat belt, or with LATCH , we don't know if the same car seat will withstand crash forces when both systems are used at the same time. Putting two installation belts through the same belt path could put stress on the car seat shell from two different angles during a crash, causing breakage. Almost like they are fighting against eachother. Using two installation belts could also concentrate more crash force on a small area of the car seat. So, in a nutshell, it hasn't been tested that way, but each one has been tested individually. The main rule is to follow the guidelines from the manufacturer. When you install the car seat using methods not outlined in the instruction manual, you are, in a way, using your child as the crash test dummy, because we cannot be sure of what will happen when car seats are used in ways that have not been crash tested and approved.
Double Trouble
16 years ago

The harnesses should fit snugly. There are two tests to determine if it is snug enough. The pinch test, if you can pinch it easily(up by the shoulders), it's not tight enough.
And the finger test, you should be able to only fit one finger under the straps up by the shoulder. If you can fit more, not tight enough.
In an accident the webbing on the harness is designed to stretch up to 14%. If your straps are loose to begin with, well they will only become more loose. It will defeat the purpose of having them restrained if they don't stay in the harness, right?

