had gradually risen from about A415 during the late 1700s and early 1800s to A435 during the late 1800s. Though A440 is generally the standard, some orchestras, particularly in Europe, use a higher pitch standard, such as A442. Theory Overtones and harmonics A stretched string can vibrate in different modes, or harmonics, and when a piano hammer strikes a string it excites multiple harmonics at the same time. The first harmonic (or fundamental frequency) is usually the loudest, and determines the pitch that is perceived. In theory the higher harmonics (also called overtones or partials) vibrate at integer multiples of the fundamental frequency. (e.g. a string with a fundamental frequency of 100 Hz would have overtones at 200 Hz, 300 Hz, 400 Hz, etc.) In reality, the frequencies of the overtones are shifted up slightly, due to inharmonicity caused by the stiffness of the strings. The relationship between two pitches, called an interval, is the ratio of their absolute frequencies. The easiest intervals to identify and tune are those where the note frequencies have a simple whole-number ratio (e.g. octave with a 2:1 ratio, perfect fifth with 3:2, etc.) because the harmonics of these intervals coincide and beat when they are out of tune. (For a perfect fifth, the 3rd harmonic of the lower note coincides with the 2nd harmonic of the top note.) Temperament The term temperament refers to a tuning system that allows intervals to beat instead of tuning pure or "just intervals". In equal temperament, for instance, a fifth would be tempered by narrowing it slightly, achieved by flattening its upper pitch slightly, or raising its lower pitch slightly. Tempering an interval causes it to beat. Because the actual tone of a vibrating piano string is not just one pitch, but a complex of tones arranged in a harmonic series, two strings that are close to a simple harmonic ratio such as a perfect fifth beat at higher pitches (at their coincident harmonics), because of the difference in pitch between their coincident harmonics. Where these frequencies can be calculated, a temperament may be tuned aurally by timing the beatings of tempered intervals. One practical method of tuning the piano begins with tuning all the notes in the "temperament" octave in the lower middle range of the piano. A tuner starts by using an external reference, usually an A440 tuning fork, (or commonly a C523.23 tuning fork) to