So you can tune a guitar, but you can’t tunafish… some professionals tune their guitar before each and every song.
The goal, really, is to tune the guitar to itself - maybe not exactly to A440, but such that when you play, all six strings are in tune - in relation - for playing. The new method uses harmonics and fretted notes like usual, but at different positions from what I have always used in the past (old way used mostly 5th fretted notes and harmonics).
First tune your D string to D …or what ever pitch you like. Many times I start a half step lower on the D string, near C#, to better fit my vocal range. You could use a tuner, a pitch pipe, a wet crystal wine glass or anything (like your perfect pitch) to set your D string.
D: set your perferred D pitch
From there you use the new method, in the order shown below, to tune the other five strings…
Second - three high strings > to achieve pitch, adjust the fretted notes
G: play harmonic at 12th fret of D string - play G string at 7th fret - adjust fretted G to pitch
B: play harmonic at 12th fret of D string - play B string at 3rd fret - adjust fretted B to pitch
e: play harmonic at 12th fret of G string - play e string at 3rd fret - adjust fretted e to pitch
Third/Last - bottom two strings > to achieve pitch, adjust the harmonic played notes
A: play harmonic at 12th fret of A string - play G string at 2nd fret - adjust harmonic A to pitch
E: play harmonic at 12th fret of E string - play e string open - adjust harmonic E to pitch
in short hand :: h = harmonic f = fretted
D: your preference
G: hD-12f G-7f
B: hD-12f B-3f
e: hG-12f e-3f
A: hA-12f G-2f
E: hE-12f e open