I got tired of jerking around with electronic tuners that sometimes worked and sometimes took me forever to finish tuning. I saw Bill Merchant tap an A tuning fork on his workbench, stick it between his molars and tune a bass with harmonics in about 2 minutes. I tried it and it works for me. The A-440, through bone conduction, fills your head with a tuning pitch regardless of background noise. I get my A string in tune and then use harmonics across the strings. No batteries, either.
I have a Fender brand tuner that I've used for years. It works fine but is useless on a gig with other people tuning, honking and banging. But my old standby is my 440 fork. I put it in my teeth, yes I still have them, or just touch the bottom of the fork to the belly of my bass and let it resonate. I have no actual proof, but I strongly suspect that the advent of the electric tuner ( I even have one on my iPhone!) has had a detrimental effect on the ears of a myriad of younger musicians. The upside: At least the guitars of the multitude of guitar players are in tune with themselves .