Nate, I think most of us don't know how to answer this question. We use electric tuners (A= 440, as Ken says), so we generally accept the tuner when it says we are on pitch. Of course, those tuners are not all equally accurate, though the Peterson tuner that Robin mentions is supposed to be one of the best. One of the issues with tuners is their display. Even if the mechanism inside can be trusted to 0.05 cents, the display may not be that accurate. If there are 10 LED lights equally spaced between C# and D, well, you can do the math. If there were 20 LED lights, the display would be twice as accurate, right? We often think about how easy or difficult those displays are to read, but few comment on the relationship between the display and the accuracy of the tuner in practice.
I have a couple of really accurate strobe tuners which I use at home, but when I'm out and about I trust a D'Addario violin tuner which I keep attached to my dulcimer.
My own ear varies. Sometimes it is very sensitive and I can hear very small imperfections in my tuning, even when the tuner says I'm in tune. Those times are not enjoyable because I never like the sound of my own dulcimer. But other times my ear is a bit "lazy" and anything close sounds good. That is a much more enjoyable space to be because I can just strum away in blissful ignorance.
Dusty T., Northern California
As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie
updated by @dusty: 02/03/24 12:49:19PM