Apple Watch series 7 elevetion

Hello, I am doing some research on Apple watch series 7 and 8. And my first question is if watch using just barometric altimeter to measure elevation or also using GPS to measure it?

Also what is the difference between series 7 and series 8 GPS chips? And also if barometric altimeter also the same or they differs?

Because from tech specifications both are the same and apple don't give us more data if they different some how or not?