Over time and use the tension on the strings will change but when you retune the tension will return to the brands stated specs. Now the strings tension properties will change over time because of the stretching that has been applied to the string. (what happens when you stretch something)Meaning how long will it hold tune because of stetching then stretching more making it easier to do so. That said at the point when ever you tune it the tension should be in a constant range.

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