As I know it, it's rated for a certain weight that we test to, but it's designed to hold way more than we test it for. We also test it horizontally at the rating, but when it's angled for us to climb, it doesn't see as much deflection. And as [USER=5796]@WARRIORWELDING[/USER] says, it has to return to how it was. I'm not super knowledgeable on the specifics of the testing, I was just one of the 5 guys that it took to get that heavy ass ladder off of the top of our rescue truck 
