Since Austria Bernd asked how to tune with a tuning fork I will try to put my method into words.
First we start with the A string of the guitar as it has the same frequency as the tuning fork.
Hit the fork and play a flageolet note on the 5th fret of the A string to get the 440Hz A.
If the string is slightly out of tune, you will start to hear a "ripple" sound which sounds kinda wavy, a bit like a vibrato. I visualised it in picture 3.
You can hear the interval until the two waves meet again. The more your A string is out of tune the faster the ripple sound will get, and the closer you get to the tuning forks' frequency the slower it becomes until it eventually vanishes when you hit the exact same frequency (picture 4).
Now, since we don't buy a tuning fork for each guitar string, we play flageolet notes on the other strings and tune them with the exact same method, we listen to the wavy ripple sound and tune the strings until the flageolet notes are on the exact same frequency.
Cons of this method:
- it takes some exercise. I for example still need ~3 minutes to tune my guitar but a friend of mine does it in less than a minute.
- you need to be in a quiet environment to be able to listen carefully to the wavy sound. if you are in a room with morons who can't stop fapping with their fucking guitars for 5 minutes so everyone can tune, you can't use this method. Sadly these morons are 90% of musicians I know.
Pros of this method:
- it is very, VERY accurate, mastering this will make you tune your instrument a lot better than with an electronical device, this is the biggest pro
- you don't need to rely on an electronic tuner anymore and we all know how often we forget to exchange their batteries or even forget them at home
- you actually don't even need a tuning fork (if you don't have one at the moment) as you can pick any random frequency and use it as a starting point. mastering this method allows you to tune your guitar even if you are alone in the nature without anything.
- it is cool as fuck to listen to and you can flex in front of other noob musicians who will suck your balls dry to teach you how to tune like this.
If you are interested, I can try to record the rippling effect when I tune my guitar this evening.