I think we all know that the readings on the cardio machines are inaccurate, so what I do is that I watch my heart rate and I just put the number along with how long I run. But yesterday I was running for 90 minutes and my heart rate was anywhere from 120 to 190-200, so at the end of my session the treadmill said that my average heart rate was 180. So what do I do? Do I put 180 for 90 minutes? Or I take everything on its own and add it up, like 120 for 30, 150 for 20, 180 for 10 etc etc? What would give me a more accurate number?