12th fret in regards to tuning?

In the first tuning lesson and later in the tuning lesson using the online tool he mentions something about the 12th fret. He uses it a few times very quickly, in fact he flies through it so fast I have no idea what he is trying to say. He just uses it a few times saying "perfect".

Whats perfect? Whats that all about? Could I get some clarification on what that has to do with tuning and how it can be used? I am also wondering if other tuning techniques will be covered later. Thanks in advance.

If it helps I just signed up for a year pre-paid. I am rather sure I can tune the guitar enough with the lesson as is but I wanted to point point this 12th fret business is mentioned and when something is mentioned I feel it must have some use and its REALLY glossed over so fast I have no idea how to use it.

Thanks again.

DaCuda, I didn't see the lesson you are speaking of, but I can give you a heads up on the 12th fret. For instance - when you tune a string, we'll use the open "E" on the 6th string to make it easier, the note should be the same on the 12th fret as it is open. Pluck the 6th string and look at the note on your tuner, it should be an "E". Now go to the 12th fret and pluck the string it should still be "E". If it isn't the same then the intonation needs to be adjusted. I would leave this to a professional because a guitar can sound really bad if it isn't done right. I still let my guitar tech do this for me and I have been playing close to 40 years!
The 12th fret also has strong harmonics, Place your index finger across all 6 strings like a bar and touch the strings with your index finger very lightly and strum all the strings. This is a harmonic and these are also used for intonation. Hope this helps. John

Thanks for the reply, I decided to watch all the core lessons that night and after watching it a few times I kind of grasped what he was saying with the harmonics and your explanation helps clear it up. I also realized I should have posted this in a different forum.

Thanks for help.