usual to play inverted chords on the guitar when they are not part of the harmony, since the bass guitar can play the root pitch. Alternate tunings There are many alternate tunings. These change the way chords are played, making some chords easier to play and others harder. Open tunings each allow a chord to be played by strumming the strings when "open", or while fretting no strings. Open tunings are common in blues and folk music, and they are used in the playing of slide guitar. Drop tunings are common in hard rock and heavy metal music. In drop-D tuning, the standard tuning's E-string is tuned down to a D note. With drop-D tuning, the bottom three strings are tuned to a root–fifth–octave (D–A–D) tuning, which simplifies the playing of power chords. Regular tunings allow chord note-forms to be shifted all around the fretboard, on all six strings (unlike standard or other non-regular tunings). Knowing a few note-patterns—for example of the C major, C minor, and C7 chords—enables a guitarist to play all such chords. "Learn a handful of chord forms in a regular tuning, and you'll know hundreds of chords!"</ref> Open tunings An open tuning allows a chord to be played by strumming the strings when "open", or while fretting no strings. The base chord consists of at least three notes and may include all the strings or a subset. The tuning is named for the base chord when played open, typically a major triad, and each major triad can be played by barring exactly one fret. Open tunings are common in blues and folk music, and they are used in the playing of slide and lap-slide ("Hawaiian") guitars. Ry Cooder uses open tunings when he plays slide guitar. Open tunings improve the intonation of major chords by reducing the error of third intervals in equal temperaments. For example, in the open-G overtones tuning G–G–D–G–B–D, the (G,B) interval is a major third, and of course each successive pair of notes on the G- and B-strings is also a major third; similarly, the open-string minor-third (B,D) induces minor thirds among all the frets of the B-D strings. The thirds of equal temperament have audible deviations from the thirds of just intonation: Equal temperaments is used in modern music because it facilitates music in all keys, while (on a piano and other instruments) just intonation provided better-sounding major-third intervals for