Good to know. When I last had lessons it was some time in the mid to late 1980s. Back then they told us ABCs: Airway (check for obstructions), Breathing, and Compressions. They emphasized compressions. They said not to press too high up on the sternum because it wouldn't work as well and not to press too low because it could break off the triangular piece of bone at the end of the sternum. That piece of bone can cause damage by cutting into organs. What they didn't really make clear was how to estimate how long someone's sternum is with their shirt on. I think the idea was to press hard enough to flex the sternum, but not hard enough to crack ribs. They really didn't explain things well enough in a lot of ways, probably because they sensed a lack of interest in most of the class.