References - Online
Bass guitar
http://en.wikipedia.org/wiki/Bass_guitar
Charango
http://en.wikipedia.org/wiki/Charango
Chords (music)
http://en.wikipedia.org/wiki/Chord_(music)
Chord Notation
http://en.wikipedia.org/wiki/Chord_notation
Circle of Fifths
Guitar
http://en.wikipedia.org/wiki/Guitar
Guitar Chords
http://en.wikipedia.org/wiki/Guitar_chord
Guitar Standard Tuning
Intervals (music)
Inversions (music)
http://en.wikipedia.org/wiki/Inversion_(music)#Inversions
Jazz Chords
http://en.wikipedia.org/wiki/Jazz_chord
Keyboard
http://en.wikipedia.org/wiki/Musical_keyboard
Mandolin
http://en.wikipedia.org/wiki/Mandolin
Notes and Note names
http://en.wikipedia.org/wiki/Note#History_of_note_names
Piano
http://en.wikipedia.org/wiki/Piano
Piano Key Frequencies
http://en.wikipedia.org/wiki/Piano_key_frequencies
Progressions (music)
http://en.wikipedia.org/wiki/Chord_progression
Roman Numeral Analysis
http://en.wikipedia.org/wiki/Roman_numeral_analysis
Requinto
http://en.wikipedia.org/wiki/Requinto
Scales (music)
http://en.wikipedia.org/wiki/Scale_(music)
Stringed Instrument Tunings
http://en.wikipedia.org/wiki/Stringed_instrument_tunings
Ukelele