The 6 points are sholder, lap,leg.
80% of your mass is usually in your butt and upper legs.(your size may vary) A single crotch will cross your eyes but is easily understood and not a good idea.
The 7th strab down at an angle to pull tension against the shoulder straps will help to keep you from going the other way. Without it the shoulder harness will just roll up with only the side tension from the lap belt to provide the holding.
The least space you have to move around is up and wour head an neck are at the highest risk.
Keeping you in the protective limits of the vehicle is their job, Staying in the fitted curve of the seat is aided by the second belt with another buckle.
You spend a lot more time needing it in a crash than the extra time would be to use it.
<small>[ March 31, 2005, 05:42 PM: Message edited by: JackD ]</small>