Adjusting intonation on a guitar is the act of making your guitar play in tune along the entire length of the fingerboard. This is accomplished by making horizontal adjustments to the guitar bridge. Intonation is affected by (a) the position of the bridge, and (b) the thickness and/or material of the strings.

If you have an acoustic guitar which does not allow horizontal adjustments, the only (economical) way of correcting the intonation is to use different strings.

You will need: a precise electronic tuner. While it is possible to adjust intonation 'by ear' it is not very precise and therefore not recommended.

First, put new strings on your guitar. Oxidated or dirty strings will often not be consistent along their length. This is also why you should change strings with some regularity. We recommend changing strings at least every six months - more often if you play professionally.

Set the guitar on a flat surface and tune the first 'E' string exactly to 'E'. Now press the string down at the 12th fret (the octave mark). Observe the reading on the tuner. If the reading is sharp (higher than 'E'), you will need to move the bridge backward (toward the base of the guitar). If it is flat (lower than 'E') you will need to move the bridge forward (toward the frets). This is accomplished by turning the adjustment screws with either a small flat screwdriver or allen wrench. Adjust it until both the open note and the fretted 12th fret note read exactly the same.

Repeat this procedure for the remaining strings, except you will be tuning to the appropriate note instead of 'E'.

What to do if your bridge does not adjust enough to make the guitar play in tune at the open position and the twelfth fret? There are only two options: (1) physically move the bridge (usually requiring expensive shop work), or (2) use a different string gauge. If the bridge position is at its extreme back setting (toward the base of the guitar) and the twelfth fret reading is still sharp, you will need to use a lighter gauge string. If it is at the extreme forward setting (toward the fingerboard) and the twelfth fret reading is still flat, you will need to use a heavier string. This is also how you would correct the intonation on an acoustic guitar which does not adjust.

You may find that you are forced to use strings which are not comfortable to play. This is understandable; however you must then make some personal decisions. Would you rather have comfort, or would you rather the guitar sound good? Most people would prefer playing a guitar that sounds great, but it is understandable (especially for students) if you find that ease of playing is the better choice for you.

A guitar will never be precisely in tune along the entire fingerboard and across all the strings. Some frets will always be a couple of cents (hundredths of a note) off. The reason has to do with an effect called temperament, which basically involves the amount a string is bent in the vertical dimension to push it down to the fingerboard. The best that you can ever do is to adjust the intonation so that it is reasonably close. The lower the action (or string height), the closer to perfection it will be. This is also the reason that tuning your guitar using the fifth and seventh fret harmonics is less accurate than fretting the notes at the fifth fret (fourth on 'B') for tuning purposes. These are topics for a future How-To note.