On a properly setup guitar, with a good tuner, an open note (say, the open D string) will ring exactly the same on the tuner as the 12th fret on the same string. If the 12th fret note is a little sharp, then your string length is slightly too short. If the 12th fret rings a little FLAT, then the overall string length is too long. The adjustment for this is at the bridge/saddle.
Acoustic guitars don't have such an adjustment, but almost all electrics do. It's the saddle itself (the part of the bridge the string physically goes over on its journey to the neck) and usually each of them will have an adjustment screw.
In the image below, #1 is where the string passes over (I used a Floyd Rose because it's the bridge on the Syn Customs), and #2 is the adjustment screw. As you can see, most of the time the adjustment screw is UNDER THE GODDAMN STRING, so this is something that is a royal pain in the balls to adjust. There is a tool to make it easier to do on a Floyd, but they're expensive and only have the one job.
On most other bridges, you have a spring-loaded adjustment screw that is much easier to work with.
On any guitar, intonation adjustments will be a part of a basic guitar setup performed by a tech. You can also make these changes at home, if you have the proper screwdriver and an accurate electronic tuner, though I don't recommend doing this yourself on a Floyd-equipped guitar, unless you've already done it many times on another style of bridge and fully grasp the practicalities of how it works and how the adjustments work.
A properly intonated guitar will allow you to play complex chords above the 12th fret that still sound perfectly in tune. A poorly intonated guitar may not be especially noticeable playing single notes, but will become hard to listen to when you play some chords that your ears are well-accustomed to.
I expect questions.
Acoustic guitars don't have such an adjustment, but almost all electrics do. It's the saddle itself (the part of the bridge the string physically goes over on its journey to the neck) and usually each of them will have an adjustment screw.
In the image below, #1 is where the string passes over (I used a Floyd Rose because it's the bridge on the Syn Customs), and #2 is the adjustment screw. As you can see, most of the time the adjustment screw is UNDER THE GODDAMN STRING, so this is something that is a royal pain in the balls to adjust. There is a tool to make it easier to do on a Floyd, but they're expensive and only have the one job.
On most other bridges, you have a spring-loaded adjustment screw that is much easier to work with.
On any guitar, intonation adjustments will be a part of a basic guitar setup performed by a tech. You can also make these changes at home, if you have the proper screwdriver and an accurate electronic tuner, though I don't recommend doing this yourself on a Floyd-equipped guitar, unless you've already done it many times on another style of bridge and fully grasp the practicalities of how it works and how the adjustments work.
A properly intonated guitar will allow you to play complex chords above the 12th fret that still sound perfectly in tune. A poorly intonated guitar may not be especially noticeable playing single notes, but will become hard to listen to when you play some chords that your ears are well-accustomed to.
I expect questions.
