I certified as an EMT 18 years ago and yes, amazing how something as simple as mechanical compressions and ventilation can continue to change and vary so much. Quite a bit has phased out to make it easier. You used to have to check pulse in the carotid artery, verify none, then measure with index and middle finger together from the bottom of the sternum to find where to start compressions and the compressions were FAR slower than they are now.
It was found that most people struggle to find the site in the neck where one would feel a pulse. That was further exacerbated in victims who had no pulse to begin with. Victims were dying because people were spending too long searching for pulses and measuring a point on the chest. To make it worse, there were a lot of people with low risk tolerance who were unwilling to provide mouth to mouth (you'd be surprised how many people think you can get HIV through saliva.)
The result was a ton of studies that show that even at the very least, chest compressions should be maintained and, if one chooses, to not provide mouth to mouth (or mouth to pocket mask, etc.) and to just aim for the center of the chest and pump.
Having done CPR, the brutal honesty is that once you start compressions, your hands will always return to the same site after you give breaths...because there will be an indentation from the first round of compressions. Broken ribs are a consequence of CPR (with some exception to children who have more flexible bones, but you still might get what is called greenstick fractures where a bone fractures on one side but not completely through and through.)
I detail these things because when someone does CPR for the first time and they haven't been told about the breaking bones and resulting crepitice, they freak out and stop. My EMS instructor told our class the same thing and I'm glad she did because the expectation was there. First time I did CPR it wasn't a surprise.
