I was having a look at the price list of a “rival” guitar tech the other day, and they mentioned their “deluxe” setup, where they say:

“Intonation is set with a digital strobe tuner which is accurate to 1/1000 of a semi-tone.”

This is something that I see a lot. Quoting BIIIG numbers of tuner accuracy like it’s something that’s desirable. There are 100 cents in a semitone (1 fret). They’re quoting accuracy to ONE THOUSANDTH of a semitone. I’m here today to tell you why this is basically just a marketing gimmick designed to confuse you and pull the wool over your eyes.

So first, let’s look at what “setting the intonation” is all about.

So a guitar is a fretted instrument. We take the scale length (the theoretical length of the string), in the case of a Strat it’s 25 1/2 inches (647.7mm). Then we use the magic number 17.817 to calculate the position of the frets.

If you divide any scale length by the constant 17.817, you will get the distance from the front edge of the nut to the first fret. Then you take the distance from the first fret to the bridge and divide that again by 17.817 to get the distance from the 1st fret to the 2nd fret and so on, until all the fret distances are calculated. Then you hammer your frets into the board and you’ve got something approximating a fretted instrument. Lovely.

So, you play an open string and tune it accurately. Then, when you fret a note, you SHORTEN the vibrating length of string, and because of the magical properties of the 17.187 number, the note pitch is increased by one semitone.

All nice and easy so far?

The problem is, when we fret a note, we arent just shortening the vibrating length of string. We also have to push down on the string to make it touch the fret, and this stretches it a little, making it go sharp. We may also apply further pressure to hold the the string in place (like you’re pressing the string right down onto the fretboard) making it go sharper still.

So, how can we compensate for this so that all of our fretted notes aren’t sharp? Well, we move the bridge saddles AWAY from the fretboard a little. This lengthens the scale length relative to the fret positions, and makes the fretted notes flatter to compensate for the stretching/pressing, without affecting the open strings (cos you tune those first).

So how do we set the intonation?

1) Play the open string
2) Tune it perfectly
3) Fret the note at the 12th fret (we use the 12th cos it’s an octave above the open string, and is in the middle of the string)
4) If the 12th fret is SHARP – move the bridge saddle AWAY from the fretboard
5) If the 12th fret is FLAT – move the bridge saddle TOWARDS the fretboard.
6) Go back to step 1 and repeat til all the strings are intonated.

Now our guitar will play in tune all over the fretboard won’t it? So why wouldn’t tuning and intonating with 1000th semitone accuracy be a GOOD thing?

Well.

Basically, all you’ve done is intonate the guitar to play in tune at the 12th fret when YOU (or someone) frets the notes with the exact amount of finger pressure that you used when you set the intonation. If someone with a lighter touch does the same, the notes will be a bit flat because they aren’t stretching the string as much. If someone with a heavier touch does it, the notes will be sharp because they’re stretching the string MORE. Do YOU always fret notes with the exact same amount of pressure? No, thought not.

Secondly, now take the guitar you just intonated perfectly at the 12th fret and play some notes at other frets. 3rd. 5th. 7th. 15th. You get the idea. Notice something? Yep – they all vary in pitch slightly. Some will be bang on, some will be a couple of cents sharp, some a couple flat.

Intonation is a COMPROMISE.

Intonation is a FUDGE.

Fretted instruments are fundamentally not super accurate. You can’t fix this with a tuner that’s accurate to 1000th of a semitone. Even a guitar that’s intonated perfectly for you at the 12th fret with only be accurate to maybe 25th of a semitone between the sharpest and flattest notes on the fretboard.

I use a SNARK clipon tuner to do my intonation, and it’s perfectly adequate for the task. I got the newer USB rechargeable version too (thought it would save me a fortune on batteries) but it turned out to be nowhere near as good. Typical!

1000th of a semitone my arse.