A little lesson on physics and music:
Let's have a piano string giving 440 Hz. The first overtone is sounding because the two halves of the string are also vibrating. But because the string have some thickness, the node on the middle has not zero length and the vibrating halves are a little bit shorter than the 1/2 string. Because of that those halves vibrate on a little higher frequence than expected, lets say about 880.5 Hz or something. Q.E.D.
Let's have a piano string giving 440 Hz. The first overtone is sounding because the two halves of the string are also vibrating. But because the string have some thickness, the node on the middle has not zero length and the vibrating halves are a little bit shorter than the 1/2 string. Because of that those halves vibrate on a little higher frequence than expected, lets say about 880.5 Hz or something. Q.E.D.