The Rough Guide to Classical Music (2010 5 ed). p. 26 Top.
Tuning & Temperament
A central tenet of music-making is the desirability of singing or playing “in tune”, accurately producing sound waves that vibrate at the correct frequency. In practical terms, this means different things to different types of musician. Singers, violinists, trombonists and others who can slide smoothly between an infinite number of pitches rely on their ears and fingers to “tune” each as they go along; keyboard players simply call in a professional tuner every few months; while harpists, according to Stravinsky, ”spend 90 percent of their lives tuning … and 10 percent playing out of tune.” [I bolded.] For all this, tuning is today a highly standardized affair. An F sharp in Madrid is the same as an F sharp in Melbourne, and pianos in New York are tuned using the same system as those in Paris or Tokyo. But it wasn’t always so simple, as modern tuning relies on two basic principles, both of which took centuries to establish their global hegemony.
What's offbeat or outlandish about tuning harps, as Stravinsky insinuates?