I compared a series 4 Apple Watch to my Garmin chest strap HRM and they gave pretty much the same readings. The Apple Watch was well within practical usability

I compared a series 4 Apple Watch to my Garmin chest strap HRM and they gave pretty much the same readings. The Apple Watch was well within practical usability for training at the gym. I can't speak to the quality of the following series, but if that isn't good enough, what is?