Have used the relative harmonic tuning technique since I started playing in the mid 70's. Beauty of this is that you can tune to an out-of-tune acoustic instrument (like a piano) and at least be "out-of-tune" together. Can't do that with any electronic tuner (or even the old faithful A 440 dial tone method, which is a terrific way of finding your baseline tuning.) AND, no worry about having dead batteries in your tuner.
Surprised at how many players depend exclusively on electronic tuners. Old school rules!