The piano is the best loved of musical instruments, thanks in part to the elegant symmetrical design of its ivory and ebony keyboard, relative to pitch. And yet this equal temperament tuning was once a hugely controversial proposition. For hundreds of years, musicians, craftsmen, church officials, heads of state and philosophers fought heatedly against the introduction of equal temperament tuning. Stuart Isacoff recounts this great battle over the best way to create music - one that culminated in the decisive victory of piano over harpsichord.