I was sitting on the couch, noodling away and my line of sight was looking through the strings at the tube. The G string sounded a little off so I used the standard method of tuning when I happened to notice that the strobe of the TV revealed the oscillations of the strings quite well. Hmmm, I thought. Sure enough I can visually tune my guitar by getting the string oscillations to match frequency while still using the standard method of tuning the strings to match the previously tuned string. I don't know if the A string is at 440 but the guitar is tuned to itself perfectly!