On: Google adds a guitar tuner to Search

[Joeboy]

Tuning a guitar (or other stringed instrument) so that the strings are more or less in tune with each other is a really basic skill that even very amateur players can mostly do. Being able to tune to an absolute pitch without any kind of reference is kind of freakishly rare.

[TedDoesntTalk → Joeboy]

This. Use harmonics after getting the A from an external source.