"You educate your ear through practice." Yes indeed - and using an electronic tuner can be a very good way of training your ear to recognise notes, so as to be better able "to tell whether your instrument is in tune, identify where it's out and put it right".

Incidentally, using harmonics is a very handy way to check that you are in (relative) tune, and to get back into tune again - but an instrument tuned purely through harmonics is actually not going to be exactly in tune