Strings go sharp after sitting for a couple days

temperature changes, perhaps?

It's been going on for quite a while, I don't think it's the change.... happened with new and old strings alike.

+1 on temperature changes as the most likely cause.

Guitars are made up of lots of different materials - wood, metal, plastic, adhesives... and different types of each. They've all got different coefficients of expansion, so they react to temperature changes at different rates, which changes the tuning.

Since you're always a touch sharp, there's no danger. If there were structural problems - a failing joint, loose screws, slipping tuners etc. - the string tension would make it go flat.

It could also be humidity changes, which can make the wood swell or shrink. But it's not likely the humidity keeps going up night after night. I'm thinking you've probably got a programmable thermostat that lowers the temperature at night? The strings contract a bit more than the wood, raising the tension and making it a touch sharp in the morning. You probably only notice it if the guitar hasn't been touched in a couple days, because your first thought is to check the tuning... but if you check the tuning every day, you'll probably find the same thing.

With steel strings on a wooden guitar, the strings go sharp when it cools down. The thermal coefficient of expansion of the steel in the strings is much greater than that of wood, so they shrink more and get tighter. I've got a couple of brass bodied resonators that behave oppositely, going flat with cooling and sharp with warming, as the brass guitar bodies expand and shrink faster than the steel strings do. They're pretty insensitive to humidity changes, though.

Thanks guys, I won't worry about it. It doesn't go that off, but it was just a bit concerning.

I don't have a programmable thermostat, but my wife does change the temperature....alot... :?

It's just odd that it's the only guitar that it happens to.

Wives will do that. Mine shoves the thermostat up and down in about 10 degree increments.

With steel strings on a wooden guitar, the strings go sharp when it cools down.<...>

And as the air cools down, saxophones go flat. It has something to do with the speed of sound relative to the temperature.

The result is, the sax player has to keep readjusting his/her tuning in a guitar band when the temperature changes. Why? Guitars have 6 strings, sax gets tuned with one adjustment to the mouthpiece's position on the neck.

I've been in a lot of guitar bands so I know ;-)

Once an electronic keyboard is introduced, everybody but the keyboard has to adjust their tuning when the weather changes on a gig.

BTW, when I get to the gig, I open the guitar and sax case and let them adjust to room temperature while I'm setting up the PA system.

Another thing that could be affecting you (less likely than temperature) is binding in the nut. Since we are all taught to tune up to pitch, if the nut is binding, there should be more tension on the tuner side of the nut. As time goes on, this should equalize pulling the strings through the nut a bit more, causing them to have more tension on the playing side of the nut. (I always put pencil graphite on the nut when I change strings.)

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