A good accurate tuning fork for guitar. Nice quality, especially for the price. I tested it against my electronic tuner and it was exactly right. I'm learning to tune by ear again after years. Surprisingly fun! The note is the same as the harmonic at the fifth fret on the A string. Tap the tuning fork, pluck the harmonic on the A string, then put the base of the fork on the guitar top. Then you can hear any differences between the two pure notes side by side.