Here is the specific complaint this page is for. You tune all six strings carefully. The open chords sound right. Then you play a D at the second fret, or a barre chord at the fifth, and something is faintly, maddeningly wrong — not wildly out, just sour enough that you keep glancing at the tuner and finding nothing to fix.
That is intonation, and it is a different fault from a guitar that will not hold its tuning. If your pitch drifts while you play, the cause is at the nut, the tuner post or in strings that have not settled, and a guitar that will not stay in tune works through those. Intonation is the opposite problem: the guitar holds pitch perfectly well, and the pitch it holds is wrong as soon as you leave the open strings.
What the word actually means
Fender publishes the clearest one-sentence definition we found:
"When we intonate a guitar we shorten or lengthen the active vibrating length of a string so that it will be in tune with itself, given the scale length of the instrument, as well as differences in string gauges and micro-variations from string to string which occur in the manufacturing process."
Two things follow from that. The first is that intonation is relative — Fender writes that the aim is for the instrument to be "in relative tune to itself", and a guitar can be perfectly intonated and still be a tempered instrument that never sounds mathematically pure. Fender says so outright in its own procedure: "Remember, guitars are tempered instruments!"
The second is that string gauge is part of the equation. Change to a heavier set and the correct saddle positions change with it. Fender publishes the consequence as a rule: "Always check and adjust the intonation as needed after every change of strings."
Three things to do before you measure anything
Fit new strings. Taylor is explicit about this, and it is the step most people skip: "We recommend that players change their strings before consulting a service technician to adjust their intonation, since guitar strings naturally lose some elasticity with time and wear." Peterson goes further and lists "a set of new strings" among the items you need before you start. Old strings give you a reading of an old string, and you will chase it.
Get the action and relief right first. Fender puts intonation last in its own setup order, and says why in one line: "Adjustments should be made after all of the above have been accomplished." String height changes how far you stretch a string to fret it, which changes the pitch of the fretted note, which is the very thing you are about to measure. If the action is high, fix that first — action that is too high and fret buzz cover the two directions that can go wrong, and action gauges covers measuring it.
Hold the guitar the way you play it. Peterson publishes this as a working instruction, and it is the detail that separates a reading you can trust from one you cannot: "Lay the guitar flat on a bench to adjust it, but always check the intonation with the instrument in the playing position, as the readings will be visibly (and later audibly) different." The same page adds "Remember to fret the string using the pressure that you would normally apply while playing", and Fender says the same thing from the other side — "make sure you are depressing the string evenly to the fret, not the fingerboard".
On an electric there is a fourth: Peterson publishes "Lower the pickups away from the strings to avoid 'doubling' and electromagnetic pull". A magnet close to a vibrating steel string pulls on it, and the tuner reads the result.
The test everybody publishes — and the one Peterson disputes
The standard check is the twelfth-fret comparison. Fender publishes it verbatim in the Stratocaster setup guide:
"Check each string at the 12th fret, harmonic to fretted note (make sure you are depressing the string evenly to the fret, not the fingerboard). If sharp, lengthen the string by adjusting the saddle back. If flat, shorten the string by moving the saddle forward."
The direction rule, which is the part people get backwards| What the tuner shows at the 12th fret | What the string needs | Which way the saddle moves |
|---|
| Fretted note SHARP of the harmonic | To be made longer | Back, away from the neck |
| Fretted note FLAT of the harmonic | To be made shorter | Forward, toward the neck |
| Fretted note matches the harmonic | Nothing | Leave it alone |
Here is the interesting part, and it comes from the one company that publishes a document devoted to this job. Peterson describes the twelfth-fret method, then says plainly: "While the above is a common system, it is not always the most satisfactory." Its preferred alternative uses the fifth and seventeenth frets instead: "Tune a string at the 5th fret. Check the string at the 17th. If sharp, move the saddle back, thus lengthening the string. If flat, shorten the string by moving the saddle forward."
That is still an octave apart, so the arithmetic is the same, but both readings are now fretted notes taken in the part of the neck where you actually play chords. The twelfth-fret harmonic is a lovely clean tone that you never use in a song. If you have a tuner that can resolve it, the fifth-and-seventeenth check is the more honest one, and Peterson is the only manufacturer we found that says so.
Electric or acoustic: this is where the page splits in two
On most electrics, this is a screwdriver job. Each string has its own saddle with its own adjustment screw, so the direction rule above is directly actionable. Work one string at a time, retune after every move, and expect to go round two or three times. Fender ends its procedure with exactly that: "Re-tune, play and make further adjustments as needed."
On most acoustics, you cannot adjust it at all.Taylor publishes why, and it is worth understanding rather than just accepting. An acoustic has one saddle serving all six strings: "Most saddles are placed at a slight angle to the bridge, which adds length to the lower strings to adjust for differences in string thickness. Likewise, many saddles are made with compensation points for some or all of the strings, which helps fine-tune those points even more." The compensation is built into the shape of the bone or synthetic blank at the factory. There is no screw.
Changing it means changing the saddle itself. Taylor: "A skilled guitar technician can cut more accurate notches into the saddle, effectively adjusting the intonation of each string by changing the string's distance from the nut." Peterson agrees and adds the warning in its own note: "Changing the saddle by filing or adding bone & glue is a job best done by an experienced luthier or instrument technician."
So on an acoustic the useful outcome of this page is a diagnosis, not a repair. You establish that intonation is genuinely the fault, you rule out old strings and high action, and then you hand a technician a specific complaint with measurements instead of "it sounds funny". Peterson is blunt about how much of the rest is you: "much of the intonation is in the hands of the player, since most acoustic guitars have non-adjustable string saddles."
One acoustic family is the exception, and it shows how fine the tolerances are. Martin's service documents for its SC models — the ones with the Sure Align neck — publish an actual intonation setscrew reached through the soundhole, with a published sensitivity figure.
2–3 cents
The intonation change from ONE full rotation of the setscrew on a Martin SC, per Martin's own service document
Martin's procedure also says to detune roughly two full steps first, that the screw must ONLY be adjusted without string tension, to torque the dovetail bolts back to 25 inch-pounds, and to recheck on a strobe tuner. Its header warns that failing to follow the directions may result in damage not covered by the warranty.
Two things to take from that number. One rotation of a screw moves the pitch by two or three cents — so the adjustments that matter here are genuinely small, and a tuner that rounds to the nearest cent is rounding away a third of your adjustment. Two: Martin publishes that procedure under a "For Authorized Martin Dealer and Service Center Use Only" header. Read it to understand the scale of the job, not as an invitation.
How accurate does the tuner need to be?
We went looking for a published answer and there is not one. No guitar maker and no tuner maker publishes a required minimum accuracy in cents for setting intonation. Fender's tools list for a full Stratocaster setup says only "Electronic tuner". That is the honest state of the published record, and anyone who tells you a specific cents threshold is inventing it.
What makers do publish is two useful things. Martin names a tuner type — its procedure step six reads "Tune to pitch and recheck intonation on strobe tuner" — and it is the only guitar maker in this research that specifies one. And the tuner manufacturers publish their own resolution, which lets you compare.
Published accuracy figures, from each manufacturer's own specification| Tuner | Published accuracy | Published for intonation work? |
|---|
| Peterson StroboClip HD | 0.1 cent, detection and display | Yes — Peterson publishes an intonation guide |
| Korg Pitchclip 2+ | ±0.1 cent in strobe mode | No |
| Boss TU-3 | ±1 cent | No |
| Korg Pitchclip 2 | ±1 cent | No |
| Snark ST-8 | Not published | No |
The Peterson distinction is the one worth reading carefully, because it is a real difference and the company explains it: "unlike other tuners which list the detection accuracy as the main specification, the StroboClip HD detection AND display accuracy is 0.1 cent due to its high definition display." A tuner can detect a fine difference and then show it to you rounded off, which is useless for a job where one screw rotation is worth two or three cents.
Peterson also publishes two setup details for this task that no guitar maker mentions: set the tuner to Equal temperament from the Sweetener menu rather than an instrument-specific sweetening, and "Check intonation frequently, especially when changing strings and especially prior to recording."
If a saddle is miles out: Fender's rough-in method
Fender publishes a second procedure, headed "INTONATION (ROUGHING IT OUT)", for getting saddles into the right neighborhood before fine-tuning by ear and tuner. Measure from the nut to the center of the twelfth fret, double it, and set the first-string saddle so the string length matches that figure. Then step each subsequent saddle back by roughly the gauge of that string — for an .011 second string, .011 further back — with the fourth-string saddle ending up parallel with the second.
It is a starting position, not a finish. But it is the fastest way to recover a bridge somebody has already had a go at, and it needs a ruler rather than a tuner.
What setting intonation will not fix
It will not fix a guitar that drifts out of tune while you play — that is nut binding, string settling or a tuner post, and it has its own page. It will not fix buzzing. It will not fix a warped or twisted neck, and it will not make a barre chord easier. It also will not make chords in the first three frets perfect, because open-position chords on a tempered instrument have their own compromises baked in.
And if the fault comes back within a week or two of being set, the strings are the first suspect again, followed by the nut. A guitar whose intonation will not stay put has a different problem from one that was simply never set. Does my guitar need a setup is the five-minute triage that tells you whether intonation is really the thing to chase.
What we would actually buy
If you own an acoustic: a fresh set of strings and nothing else. Fit them, let them settle, and check again. If it is still sour up the neck, you have a technician-shaped problem and buying tools will not change that.
If you own an electric and want to do this properly: the tuner is the purchase that matters, because every other tool here is a screwdriver. A tuner that publishes 0.1 cent on both detection and display is the difference between setting intonation and guessing at it.
