Karvonen method
The Karvonen method sets a target heart rate from your heart-rate reserve rather than from maximum alone: target = (HRmax − resting) × intensity + resting. Published in 1957, it is still the standard way to produce zones that reflect resting fitness.
Example
The same 70% intensity gives 133 bpm by plain percentage-of-maximum and 151 bpm by Karvonen for someone with a resting rate of 60. That is not a rounding difference.