In tuning, the meantone system was a common technique used for keyboard instruments before equal temperament came into general use. Meantone temperament is a tuning in which the thirds are turned pure, and all of the fifths are one-fourth of a diatonic comma too narrow. All the whole tones are equal and are precisely half a major third, hence the name meantone. It provides for the pure intonation of the key of C major and those lying near it at the expense of the more extreme sharp and flat keys, which is the reason why remote keys were rarely used in keyboard works before the adoption of equal temperament. There was, for example, a pure FA and BB, but these notes were out of tune when used as GB or AA.