Some people think tuning a pure 4:2 means tuning an octave and trying to make the 4:2 partial beatless.
That's true but it's impossible to get any kind of accuracy or precision doing it this way.
See for yourself. Tune this A3A4 octave so that the 4:2 (A5) is beatless.
I've even added a button so you can hear the filtered A5 to help.
Your results will be posted here.