They call it "target max heart rate" because that's what they want your max heart rate to be! 180-something is putting you at risk of being a statistic, and we don't want you to be a statistic.
So make it easy for yourself. Keep the timex, but also get one of those wrist bands that monitors your heart rate. That way, all you need to do is look at the read-out on the wrist band while you're exercizing (or having sex).
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