I am still new to this cardio thing so hang with me. I don't trust the monitors on the treadmills at the gym so I thought if I timed my heart beat for 15 seconds and multiplied it by 4 I would get my heart rate per minute. So I did it and came up with a constant 33 beats in 15 seconds, which means that its 132 beats a minute. My THR would be between 125-137. Is this accurate or am I just making SHIT up.