Harmonics and Overtones
The calculator shows you the even, and the odd harmonics of your fundamental frequency. Furthermore, you can see the closest note and its respective frequency. In addition to that, you will find the offset in cents. An actual overtone of a frequency does sound more harmonic than the frequency of a musical note. So in some cases, you might want to “detune” certain notes to create a more harmonic sound. (Note: With this Overtone and Harmonics Calculator you can only determine the frequencies for notes like a major 3rd or a major 5th for example. I am soon going to implement a chart of the 12TET compared to just intonation. For now, check out this article about equal temperament.)
Keep in mind that this only works for specific intervals. You cannot play the whole song by the Red Hot Chili Peppers with a detuned B string. So use this technique only when it is needed.