I just switched from a 2017 945 to a new 245 music (I know the current model is 255). I am not an athlete just a granny working on fitness but do want accurate heart rate data while I am pushing it. I tried a garmin chest strap with my old 945 and holding a pairing connection was a nightmare--the sensors on my old watch were pretty badly scratched so maybe I do not need the strap. Not sure.