This affects every note on the fret board, not just open strings because you obviously have to tune a few cents differently and the string lengths are each a tiny bit altered. Just enough. Guitars that are tough to temper are now magically in-tune up the neck. My only wish is that they were made from bone and of course less expensive. You can find them domestically now and in Japan.

This overpriced little piece of plastic may seem to help a bit - but on OPEN chords only. Put a capo on any fret and your money goes out the window. I dont know many acoustic guitar players who play every single song without using a capo at some point. You can achieve the same sense of "perfect intonation" on open chords by simply placing a small piece of a finishing nail under the b string at the nut...or use the old Bic pen top trick. Those are both free. I simply temper my tunings when I play - as one should.

Try one! These are similar to the Earvana nut, and they work! In response to the "Snake oil" review: thinking that this product only affects open notes is an easy mistake to make, but it's indeed a mistake. Take the G string for example. The product effectively moves the nut closer to the first fret, shortening the scale length of that string. So when you tune it to G, the string is slightly looser to resonate at G with the shorter length. Then the fretted notes are flatter than before. So, ironically the OPEN note is the same G you tuned to before, but the FRETTED notes are the ones being affected (opposite of the snake oil claim). And that compensation sounds sweet up and down the fretboard (mostly frets 1-8 or so). Put a capo on anywhere between frets 1 and 7, and you'll still hear the effect.

Easy to install and uninstall if need be

Makes my guitar stay in tune better.

As there is very little info online about this product, I was unsure if it was a gimmick or not. But I have an old 70's Takamine 340SD (the Martin lawsuit guitar) that plays and sounds excellent but has always had some intonation issues, particularly in open position chords, so I thought it would be worth taking a chance. Glad I did!I inserted the SOS at the nut as indicated, and first it caused a bit of buzzing at the nut, so I added two of the included shim stickers and the buzzing is completely gone. But the important question is whether it works for its intended purpose or not- happy to say it does. Careful checking of open and fretted notes with an accurate Korg tuner proved that the SOS did indeed improve intonation quite measurably. Chords sound sweeter and I no longer need to make small tuning compromises to balance things out. On this guitar, if I tuned to pitch with a tuner, an open E chord might be in tune, but the D would be pretty awful, for example. Now it's really good in all open chords as well as up type neck- really quite surprised at the difference. Definitely worth the money; another reviewer had issue with the cost- I accept that it takes time and skill to measure the correct spacing for each string, design it, source product materials, etc and that it costs a lot of money to tool up for manufacturing- plus the company needs to make a profit. Yes, it might only have 10 cents worth of plastic, but it's well worth it for the results. Twenty bucks for a guitar that now plays in tune? Beats paying a luthier to make or install a compensated nut.Two things to note- first is that as it slightly shortens the width between the nut and first fret, I noticed it takes a little more pressure to play first position notes- no big deal, just about the same as going up a gauge or two and it only applies to the first position. Second is that the SOS is about 1/2 a centimetre wider than the nut, and has pretty sharp edges, so I needed to file it down and round it off to avoid catching my index finger on it. I'm sure it's made that way so it will fit any guitar. Finally solved my intonation problem!EDIT- October 2018:Just editing here to update a bit. I recently restrung a 35-year old Vantage acoustic that I'd lent to my nephew 15 years ago, and I just got it back from him. This guitar had been busking around the world with me for years- had a broken headstock, numerous other repairs, so really a true beater. I bought it in London, where it was being used to prop up a sign in a music store- it wasn't even for sale because they thought it was such a piece of crap! I asked them if I could try it (I was looking for a cheap busking guitar in Europe), and I knew as soon as I pick dit up that it was the right guitar- I'm sure many can relate. Anyway, it's always had a really good tone and the neck is excellent to play, however the intonation was horrendous- drastic compromises to get it to sound even close to in tune over more than two open position chords; I had to tune it as normal, then drop the B string almost a quarter step and then adjust the high E to approximate chords sounding in tune. It would only sound reasonable when I was singing over top, as my vocals would mask the slightly wonky sounding chords. Then I tried the SOS-AG1 from my Takamine on it a couple of nights ago- AMAZING!!! First time this guitar has ever really played in tune! I was seriously astounded at how much better it sounded. Blew me away, seriously that much difference. I'm ordering two more of these- one for the Vantage, and one for me Taylor 2013 416 CE Spring Limited, which is an incredible guitar, but the B string is always a little sharp on open D and G chords.

This tiny thing will make enormous changes on your guitar. All the open chords like E, D and C sound perfect.If ever felt frustrated with your brand new guitar and, wonder why it was sounding off, this is your salvation!

The adjustment that this spacer makes is actually quite effective. The intonation up towards the higher frets sounds much more natural and correct as compared to just a stock nut.That being said, I feel like it's really overpriced for what you get. It's just a little tiny sliver of plastic that's wedged under the strings by the nut. I would say that the actual cost of materials would be something like 10 cents (if that). Also, because this product is only stocked by Japanese sellers (at the time of this writing), be prepared to wait upwards of a month for actual delivery.