The other three (XC, A2, and A4) have a four-point harness system with a single, round snap-style closure in the center of the chest. For one, it is convenient to have just one closure to secure. Second, the rounded snap can pivot so no matter how you adjust it, the closure will self-adjust. Each of the four straps has a certain amount of firm stretch that keeps constant tension, therefore keeping the pack from bouncing around. We’ll put some time on these and you’ll see a full test in an upcoming issue of the magazine.